人口

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The population of the world in Imperator Rome is represented by individual population units, or pops, each of whom live in a particular territory and owe their allegiance to the country that owns their home. Pops drive the economy and military of a nation and are the most important source of gold (directly through taxes and indirectly through trade, which produces commerce), manpower, and research points, but must also be kept happy and content lest they drive unrest in their province and revolt. In general, pops cannot be interacted with directly and will grow, assimilate, convert, promote, and migrate of their own accord, but the use of governor policies and the construction of infrastructure can be used to adjust the environment they live in and manipulate and control a country's demographics on a larger, more macro scale.

Social classes

A pop belongs to one of the five available social classes, or pop types. The social class of a pop is one of its most important properties and determines what a pop produces, its political weight, what happiness modifiers it is affected by, and more.

1. Nobles - generate research points and trade routes
2. Citizens – generate research points, trade routes and manpower
3. Freemen – generate manpower and tax income
4. Tribesmen – generate manpower and tax income
5. Slaves – generate tax income and additional trade goods

The class structure of a territory's population will approach its optimal ratio over time through pop promotion and demotion, the value of which is specific to each territory and varies by the territory's buildings and rank, the country's government form, local and national modifiers, and many other factors. This ratio and the rate of change can be affected by player choices, and promotion is additionally restricted by the pop's level of civic rights based on its culture.

There are also a few other effects that can directly change a pop's social class:

• When a territory is occupied, there is a chance that some pops will be immediately demoted one level: Nobles ⇒ Citizens (5% chance), Citizens ⇒ Freemen (25% chance), and Freemen ⇒ Slaves (25% chance).
• When any territory is occupied, some of its pops will be enslaved according to the army's enslavement efficiency and immediately moved to one of the occupier's territories, usually a provincial or country capital, as a new slave pop (keeping its culture and religion).
• Some events can also immediately promote or demote pops.

Nobles

Nobles represent the elites in Rome, and nobility in monarchies. Typically, they would be owners of a Latifundium.

Each Noble Pop at 100% Happiness produces per month:

• +0.5 Research Points
• +0.15 Trade Routes (not affected by happiness)

Nobles also have the following other properties:

• 3.00 Political Weight
• 0.5 Food Consumption
• -20% Base Happiness
• +0.40 Base Assimilation
• +0.40 Base Conversion
• +2 Base Demotion Speed
• +0.4 Base Migration Speed

Nobles only have a relevant desired Ratio in cities, metropolises, and the capital (even if it does not have city status). Their happiness is heavily affected by civilisation level and is in general difficult but important to manage, with both the lowest base happiness and the highest political weight of all pop classes. Both their ratio and happiness can be increased via the library, while the academy increases their ratio by half as much along with their (significant) research output.

Nobles are generally the most powerful and productive pop type and it can be advantageous to maximize the number of nobles in the country, as long as their happiness can be kept under control - their high food consumption is significant, particularly in the capital where they are concentrated in large numbers and will often outstrip the local food supply, and their low happiness and high political weight makes them dangerous if not properly appeased. Trade goods are an important source of happiness modifiers, and as they are applied-province wide it is usually best to focus most on noble ratio in cities in the capital province (which has the additional benefit of usually being primarily the primary culture).

Noble civic rights are rather exclusive, giving a combined -4% Integrated Culture Happiness malus and -5% Primary Culture Happiness for every non-primary culture, which means that granting these rights give a heavy penalty and generally only primary culture pops will have the civic right and be able to promote to nobles. However, conquered noble pops will in general remain in significant numbers and non-integrated culture noble pops can be a significant source of unrest when conquering the cities and especially capital provinces of other countries, and will additionally be slow to assimilate, convert, and demote, ensuring that they can be a persistent problem.

Citizens

Citizens represent those with a privileged legal status in Rome.

Each Citizen Pop at 100% Happiness produces per month:

• +0.2 Research Points
• +0.03 Trade Routes (not affected by happiness)
• +2 Manpower (per year)

Citizens also have the following other properties:

• 1.50 Political Weight
• 0.3 Food Consumption
• -10% Base Happiness
• +0.60 Base Assimilation
• +0.60 Base Conversion
• +6 Base Promotion Speed
• +4 Base Demotion Speed
• +0.6 Base Migration Speed

Citizens generally only have a significant desired ratio in cities, metropolises, and the capital (even if it does not have city status), though most larger settlements will usually have room for one or two citizen pops as well. Both their ratio and happiness can be increased by the court of law. Citizen civic rights are associated with integrated cultures, and only integrated culture pops will be able to promote to citizens, which can prove to be an obstacle to gaining more citizens in cities with a high non-integrated culture population.

In general, citizens can be considered a weaker form of nobles - less production per pop, but easier to feed, please, and promote to, with a higher desired ratio and a less expensive civic right. In most cities they will still make up a significant form of the population, and can be useful to focus on in cities dominated by integrated cultures that have not been given the full noble civic right.

Freemen

Freemen represent the plebeians of Rome. Artisans and small holders.

Each Freeman Pop at 100% Happiness produces per month:

• +0.005 Base Tax
• +4 Manpower (per year)

Freemen also have the following other properties:

• 1.00 Political Weight
• 0.2 Food Consumption
• 0% Base Happiness
• +0.60 Base Assimilation
• +0.60 Base Conversion
• +6 Base Promotion Speed
• +6 Base Demotion Speed
• +1 Base Migration Speed

Freemen are found primarily in cities, but also have a significant base optimal ratio (20%) in the settlements of monarchies and republics. They are somewhat easier to maintain than citizens, but about equally affected by civilisation level. While freemen produce some tax their primary contribution is as main source of manpower, so their usefulness is highly situational depending on how much additional manpower is needed (mostly medium-size countries that have enough pops to make a significant difference, while not being so large that additional manpower is not really needed). Both their ratio and happiness can be increased via the forum in cities and metropolises, and barracks in settlements, and as the default civic right in non-integrated cultures they will tend to be disproportionate represented in those areas.

Tribesmen

These represent uncivilized folks, barbarians.

Each Tribesmen Pop at 100% Happiness produces per month:

• +0.008 Base Tax
• +3 Manpower

Tribesmen also have the following other properties:

• 0.75 Political Weight
• 0.1 Food Consumption
• 16% Base Happiness
• +0.40 Base Assimilation
• +0.40 Base Conversion
• +4 Base Promotion Speed
• +2 Base Demotion Speed
• +2 Base Migration Speed

Tribesmen have a relatively high base happiness, but unlike all other pop classes receive a penalty for Civilisation level. Their production is comparable to freemen, with a focus on manpower and some amount of tax income, though actually getting those outputs is generally easier with their higher base happiness. In settlements, tribesmen output and happiness can be increased by building Tribal Settlements.

For tribal nations, they make up 50% of the Settlement Population, limiting the space available for slaves and thus trade goods and tax production. In any cities, they are less common, but still have a noticeable ratio. Tribesmen will therefore usually make up a large proportion of a tribal country's population, increasing their manpower relative to what would be expected from their population but usually with less income. Tribesmen also have a high base migration speed which means that they will move around significantly more quickly than other pop types.

For non-tribal nations, while they are technically superior to freemen the significant happiness penalties from civilization value means that tribesmen are usually much better off be promoted or demoted to one of the other classes. For these nations, they have a desired ratio of 0% at any location unless a Tribal Settlement is built, though their slow promotion/demotion speed means that tribesman-heavy territories will usually take some time to become properly useful.

Slaves

Slaves are mostly prisoners of war (POWs).

Each Slave Pop produces per month:

• +0.015 Base Tax

Slaves also have the following other properties:

• 0.35 Political Weight
• -30% Base Happiness
• 0.1 Food Consumption
• +0.60 Base Assimilation
• +0.60 Base Conversion
• +10 Base Promotion Speed
• +0.05 Base Migration Speed

Slaves are the backbone of almost every economy during the time frame of the game and the primary source of income for many countries. There is no nation or territory that does not want, doesn't need or doesn't have slaves. They are mostly found in settlements, where they have a base optimal ratio of 80% (monarchy/republic) or 50% (tribal) of the population, but are also found in significant proportions in cities. Their happiness, output and desired ratio can all be increased by the mill in territories with city status, and output by the slave estate in settlements. While slaves can appear through demotion and population growth like all other pop types, slaves can also uniquely be acquired through the enslavement of pops when occupying enemy territories, as well as through slave raiding for countries with the relevant military traditions. For many war-focused countries, enslavement can be the primary source of population growth in a nation's core territories, with slaves eventually assimilating/converting and promoting up to swell the ranks of the upper classes as well.

In addition to producing more tax income than any other pop type, slaves can also uniquely produce additional trade goods in a territory, based on the slaves needed for local surplus value of the territory. This value is a base of 15 in settlements and 20 in cities and metropolises, which can be lowered by the mine and farming settlement buildings in (as well as a large variety of other modifiers), and gives 1 extra trade good for every multiple (rounded down) of the slaves needed for local surplus in slaves there are in that territory.

Their happiness can be difficult to keep high, as those captured in war tend to be of the wrong culture and religion. Importantly, however, the output of slaves does not depend on their happiness, which means that the primary concern of slave happiness is controlling the unrest they produce, which given their low political weight is typically not too high.

Output

Depending on their class, pops produce various different types of resources, including gold, manpower, and research points, and are the often main (or only) source of these resources in the game. In addition to the output modifiers for each specific resource, the population output modifier will also increase the production of all resources produced by pops, and is in general one of the most powerful economic modifiers in the game. Pop output modifiers combine additively with resource-specific modifiers, but are combined multiplicatively with the output modifier from happiness (for classes where happiness is relevant to production). This gives the following formula for the output of each individual resource produced by a pop:

[math]\displaystyle{ \text{Pop Output for Resource}= \text{Base Pop Output for Resource} \cdot \frac{100% + \text{Pop Output Modifier} + \text{Resource Output Modifier}}{100%} \cdot \frac{\text{Pop Happiness}}{100%} }[/math]

Note that unlike with all other resources, output modifiers do not affect the number of trade routes produced by a pop, which is always constant for each pop (depending on its class).

Some of the more important sources of population output modifiers include:

• -25% in settlements
• +10% in the capital territory
• +10% in province capitals
• +1% for each Foundry (in territories with city status)
• -10% if the dominant culture in the territory is not an integrated culture
• -20% in occupied territories
• +1% for each Horses trade good in the province
• +1% for each Steppe Horses trade good in the province
• +3% for each Elephants trade good in the province
• +4% from each Provincial Procurators province investment
• -4% per governor finesse plus a base of -4% with the Harsh Treatment governor policy
• -4% per governor finesse plus a base of -4% with the Local Autonomy governor policy
• +10% in the capital province
• +2.5% per governor finesse
• +10% in the capital region

Pop output can also be affected on a class-specific basis with the local/national noble output, citizen output, freeman output, tribesman output, and slave output modifiers. Like with happiness modifiers, each of these modifiers has three different variants that determine which determine its scope - local, which only affects pops of that class in a particular territory; culture, which affects all pops of that class with a specific culture, or national, which affects all pops of a certain class in an entire country. These modifiers are in general much more common than the general pop output modifier and can come from a large variety of sources, such as buildings, trade goods, deities and omens, laws and government forms, inventions, governor traits, and more.

Happiness

File:Pop happiness - Hellenic Roman Citizen .jpg

You can find the happiness of each pop by going to the Province tab, and then hovering on the icon of one of the pops available

Happiness represents how content and satisfied a particular pop is with the current government, affecting both how much of its production actually gets collected by the state as well as how willing the pop is to support resistance - or even rebellion - against the current government. Each of the five pop types has a certain base happiness value, varying from -30% for slaves to 16% for tribesmen. Then, there are a large number of local and national happiness modifiers that are applied, including but not limited to:

• Culture
• Religion
• Civilization value
• Trade goods
• Laws
• Inventions
• Stability
• Buildings
• Ideas

In general, there are 4 different sets of modifiers that will each affect a different set of pops:

• General happiness modifiers ( (Local) Population Happiness)
• Pop class modifiers ( Noble Happiness, Citizen Happiness, Freeman Happiness, Tribesman Happiness, and Slave Happiness modifiers)
  • Each of these modifiers has three variants: Local Happiness, applied to a single territory or province; Culture Happiness, applied to pops of a particular culture; and National Happiness, applied to all pops of the specific class across the whole country
• Culture modifiers ( Culture Happiness, Integrated Culture Happiness, Unintegrated Culture Happiness, and Unintegrated Culture Group Happiness modifiers)
• Religion modifiers ( State Religion Happiness and state religion pantheon deity modifiers)

A pop's happiness is the sum of all happiness modifiers it is affected by over its base happiness value, and has a range of 0% to 100%, with 50% the median value at which they are neither content nor discontent. The average happiness of all pops of a particular class is displayed in the territory view.

Happiness has two main effects on a pop:

• Output: a pop's output (except for slaves) is scaled according its current happiness, before other modifiers are applied. For instance, a freeman pop at 50% happiness generates a base of only 2 Manpower instead of 4.
• Unrest: any pop with happiness less than 50% will generate unrest in the territory it currently resides in, scaled by its happiness and political weight, which acts as a multiplier on how much unrest it produces - for instance, an angry noble pop will produce far more unrest than a discontent slave. High unrest will lower province loyalty and may eventually lead to rebellions.

The unrest produced by each unhappy pop is scaled to the total population of the territory, the pop's political weight, and how much its happiness is below 50%, giving a formula of approximately:

[math]\displaystyle{ \text{Unrest}=10 \cdot \frac{1}{\text{Territory Population}} \cdot \text{Pop Political Weight} \cdot \frac{50 - \text{Pop Happiness}}{50} }[/math]

The total unrest for each territory is simply the sum of the unrest produced over all its pops.

Strategy

As with all modifiers, national modifiers are almost always better than local modifiers, even if the value is somewhat weaker. Even relatively small changes in happiness can have a noticeable impact on pop output or unrest generated if applied across a large enough number of pops.

Generally, the largest differences in overall population happiness are between integrated cultures and unintegrated, especially unintegrated culture group, pops, with different strategies relevant in each area. While there can be significant differences in pop class happiness, these are usually not too relevant as, for instance, slaves do not have an output difference from happiness and have a political weight too low to be particularly relevant, while for many countries tribesmen will only exist in appreciable quantities in recently conquered areas where low happiness is to be expected in the first place.

In core, primary/integrated culture and state religion areas, happiness will rarely be low enough to produce any significant unrest and the primary concern of happiness is instead to maximize pop output, as these are often the most populated and productive parts of a country. Since slaves do not change their output based on happiness, the primary focus in core areas is to maximize the happiness of the highly productive nobles and then citizens, typically by building their associated buildings in cities, importing their specific trade goods (generally only available in significant quantities a little bit into the game), and increasing civilization level (though only as a general, long term goal). Focusing on freemen happiness may also be situationally useful, but by the time a country is wealthy enough to invest in freemen it usually no longer has a pressing need for more manpower, at least as opposed to research and commerce income (from trade routes). Note that happiness is capped at 100%, which can often be exceeded by the accumulation of various bonuses by the midgame, and while it can be useful to have some buffer in case stability drops or war exhaustion increases at some point increasing happiness ceases to be useful and it can be better to invest building or trade route slots into other areas.

In contrast, recently conquered provinces of an unintegrated culture (especially of a different culture group) and different religion will be particularly difficult to please, and in general unless the country has a large number of unintegrated culture group happiness bonuses they will be virtually impossible to satisfy completely. For these areas, trying to fully manage happiness is very costly and it is easiest to just appoint a loyal, uncorrupt governor and build enough forts in the province to keep unrest and province loyalty under control in the short to medium term; if not even this is enough, the easiest way to quickly reduce the penalties from unhappiness is to try to appease any nobles and/or citizens in the province (who are normally the most unhappy as well as the largest generators of unrest), typically by building their happiness-improving buildings in the cities and/or importing the specific trade goods that improve their happiness. If stability is low, focusing on raising that can also help significantly with happiness problems. Over time pops will convert/assimilate and become happier, decreasing the proportion of discontent pops to the point where the forts may no longer be needed - building a grand theater and great temple in the main cities of the province can speed this up process significantly.

Assimilation

主条目：Assimilation

Conversion

主条目：Conversion

In every territory, a single pop can undergo conversion to the state religion at a time, as long as there are any pops in that territory that can convert and are not otherwise busy (e.g. assimilating or promoting). Outside of events, pops will always convert to the state religion. Conversion progress builds each month, with the exact progress determined by the sum of all Pop Conversion Speed modifiers. Once progress reaches 100%, the pop will be converted to the state religion and another pop will begin to convert, if there are any other pops that can be converted. The speed of conversion is influenced by many factors, particularly the Religious Conversion governor policy and the dominant province culture and religion being different from the state culture and religion. Note that it is possible for conversion to be completely stalled.

All else being equal, it is generally preferable to convert pops to the state religion, though the differences in happiness are much less than with unintegrated culture or culture group pops and can be ameliorated by adopting deities of the pop's religion in the pantheon (though this will necessarily come at the expense of the happiness of pops of other religions), which generally makes conversion less important than assimilation. Under some circumstances it may also be beneficial to retain pops of other religions in order to have continued access to their deities, though the strong effects of religious unity on omen power means that it is still generally undesirable to have too many other pops of a non-state religion.

Population Change

Population Growth

The main way that new pops appear in the game is through natural population growth. Every colonizable territory in the game will have one randomly chosen pop growing at a time, gaining progress each month according to the territory's Population Growth Speed, determined by the sum of all local and national population growth modifiers. Once the population growth progress reaches 100%, a new pop will be created in the territory with the same pop class, culture, and religion of the pop it originally grew from. Note that a pop will continue to grow even if the pop it is growing from its killed, moved away, changed in any way, which might result in a newly grown pop no longer sharing the same characteristics of the original pop once it finishes if the original pop changed in the meantime.

Important sources of population growth are listed below:

• +0.01% base value for all territories
• +0.003% per point of civilization value
• -0.03% for each pop over the population capacity
• +0.02% for every 12 months of the province's total food consumption that the province has stored, up to a maximum of 120 Months
• -0.06% for blockaded territories
• -0.01% for looted territories
• -0.20% for raided territories
• -0.25% for pillaged territories
• +0.5% for depopulated territories
• +0.03% when at peace
• +0.01% for every point of stability over 50
• +0.025% for each tier of a great wonder's Fertile Nation effect
• +0.01% with the Grain Rations ( Religious Advances 1), +0.02% with Obstetrics ( Religious Advances 10), and +0.02% with Encouragement of Migration ( Religious Advances 14)
• +0.10% as a passive modifier of many deities (+0.125% if the holy site is held)
• +0.08% per 100% omen power for many omens (+0.10% per 100% omen power if the holy site is held)
• +0.05% with the Infrastructure Policy Monarchy law
• +0.03% with   Epidauran Heritage (Epiduaros),   Halicarnassan Heritage (Halikarnassos),   Metapontine Heritage (Metapontum),   Ciusan Heritage (Kios)
• -0.01% with Euboean Heritage (cultural)
• +0.02% from governors with Gluttonous trait
• -0.02% from governors with Self-controlled trait

If aiming to boost population growth, stability (while it gives the highest potential growth rate, it is the most costly to keep high) and stored food are generally the most effective. The other modifiers are smaller and generally have a higher opportunity cost. There are also a large number of other modifiers from events, decisions, and missions that can increase or decrease population growth in a territory, most notably the Roman Warm Period.

If the population growth speed is negative - usually as a result of starvation, or sometimes significant overpopulation - pops in the territory will instead begin to die. Any pop that is growing will instead begin to lose progress, and if it reaches 0 a randomly pop will be chosen to begin dying. The progress bar will be reset to 100% and gradually lose progress according to the current population growth speed, and once the growth progress reaches 0 the pop will be killed and another pop will begin to die.

Note that population growth in general does not scale according to the actual population of the territory, but instead remains constant as the population grows (within the population capacity). This means that population growth tends to be linear over the course of the game, not exponential, and that population growth generally scales best to the number of owned territories rather than the population of a country.

Occupation

When a territory is occupied an by army led by a general, around one third of all captured pops (the amount determined by the enslavement efficiency of the occupying army) will be killed rather than enslaved and sent back to the homeland, which in a large scale war can result in a significant amount of pops that are killed. When a city, metropolis, or is occupied, the general of the army will also get an event to decide how much to sack the city, which can result in further loss of population if the general decides to let the army loose.

Pop Movement

While every pop lives in a certain territory, they are generally not directly bound to their current home and under various circumstances may decide to move, or be forcibly moved, to another territory. In addition to events, decisions, missions, and certain interactions, there are a number of mechanics by which pops can move from territory to territory, some happening passively with others depending more strongly on the country's actions.

Migration

Free pops will migrate of their own volition to nearby territories in pursuit of economic opportunities. A territory's general attractiveness for migration is represented by its migration attraction, which is determined largely by available population capacity and civilization value, but can also be decreased by disruptive actions and events such as unrest, sieges and occupation, starvation, and overpopulation, usually significantly so. Certain governor policies can also be used to some extent to adjust migration attraction.

Important modifiers to migration attraction include:

• +1 base value for all territories
• -3 for settlements
• +2 for metropolises
• +0.15 for each free slot of population capacity
• +0.05 per point of civilization value
• +2 for the capital
• +1 if the territory is a province capital
• +5 if the territory has a holy site
• +0.05 for each outgoing road in a territory
• +1 for territories adjacent to a major river
• +0.1 per level of port
• -1 for each point of unrest
• -10 if the territory is starving
• -4 for each pop over the population capacity
• -10 if the territory is occupied
• -30 if the territory is under siege
• -2 if the territory was recently looted
• +5 if the territory was depopulated
• -0.6 per governor finesse plus a base of -6 with the Harsh Treatment governor policy
• +0.1 per governor finesse plus a base of +1 in the province capital with the Centralize Population governor policy
• -0.5 per governor finesse plus a base of 5 in non- province capital territories with the Centralize Population governor policy
• -0.5 per governor finesse plus a base of 5 in the province capital with the Decentralize Population governor policy
• +0.1 per governor finesse plus a base of +1 in non- province capital territories with the Decentralize Population governor policy

All pops other than slaves are eligible to migrate as long as it is not currently busy ( assimilating, converting, promoting, or demoting), and the pop that migrates is chosen at random. Every territory can then have 1 pop that is migrating away to another territory with higher migration attraction, with pops generally preferring targets with higher attraction. There is no limit, however, to the number of pops that can be immigrating to territory at a given time, which generally results in territories with high migration attraction receiving a disproportionate share of migrants. Pops can migrate between neighbouring territories (including those with a different owner, though not to or from uncolonized territories), territories in the same province, or between more distant territories that both have ports in their province, as long as they are part of the same country.

As with all passively occurring pop activities, when a pop is emigrating it will gain a certain amount of progress each month, determined by the combined migration speed modifiers of the pop, territory (that the pop is emigrating from), and the country, with the pop moving to its new home once the progress bar reaches 100%. Each pop class has a certain base migration speed, with tribesmen the fastest and nobles and citizens the slowest, while migrating from settlements is also much slower than from cities and metropolises. Geographical considerations such as being adjacent to a river, being on the coast, and especially having a port will increase migration speed, as do factors disrupting life in the territory of origin such as unrest, overpopulation, and starvation. Migration speed can be further increased by certain laws, inventions, and governor policies, as well.

Important modifiers to migration speed include:

• +1 for nobles
• +1 for citizens
• +2 for freemen
• +3 for tribesmen
• +0.05 for slaves
• +10% for each outgoing
• -75% for settlements
• +10% for territories with a nearby river
• +25% for territories adjacent to a major river
• +0.25 if the territory is coastal
• -25% for normal winters
• -50% for severe winters
• +0.1 per level of port
• -25% from a Barracks
• -25% from a Slave Estate
• -25% from a Mine
• -25% from a Farming Settlement
• +75% from a Provincial Legation
• +25% for each point of unrest
• +10 if the territory is starving
• +3 for each pop over the population capacity
• +2.5% for each owned port in the province
• +0.1 per governor finesse plus a base of +1 with the Harsh Treatment governor policy
• +0.2 per governor finesse plus a base of +2 with the Centralize Population governor policy
• +0.2 per governor finesse plus a base of +2 with the Decentralize Population governor policy
• +10% with the Coloniae invention
• +0.05% for each point of ruler corruption
• +1.5 with the Military Settlement Policy Republic law
• +1.5 with the Lex Servilia Glaucia   Roman Republic law
• +5% with   Nabatean Heritage (Nabatea)

While seemingly quite slow, migration can be a powerful force over the course of the game, and generally gives a substantial contribution to the population growth of cities. Migration between port provinces is particularly powerful given the much larger pool of territories that immigrants can be drawn from, which makes it particularly useful to place the capital and/or other major economic centres at ports beyond the base bonuses that they give. On a smaller scale, immigration from settlements in the countryside to the local provincial capital or other nearby cities also contributes to urbanization over the course of the game, at least in settled nations; while the predominant slaves in territories cannot migrate, the local freemen can, which reduces the ratio of freemen in the settlement and, unless disabled, allows the remaining slaves to promote into their place, allowing for further migration.

Manual Movement

While slaves cannot migrate on their own, they can still be moved manually by their owner country through the territory population interface to any owned territory that either neighbours or is in the same province as the territory of origin. Tribal nations can additionally manually move owned tribesmen pops through the same mechanic as well. Unlike migration, manual movement of pops happens instantaneously with no cooldowns or other restrictions - if desired, a single pop can be moved multiple times between many different territories on the same day - though there is also a base cost of 5 gold every time a pop is moved, which for slaves can be modified by the move slaves cost modifier, available only as a -25% reduction with the vegetables capital bonus.

Moving slaves can to an extent can be used to control and manage the country's production of trade goods, as the number of trade goods is determined in part by how many multiples of the local slaves needed for local surplus value there is in the local slave population, by just generally moving them to territories that produce more desirable trade goods or more careful optimization to push a territory's slave population just over the next threshold for producing another instance of the trade good sooner than population growth would have occurred naturally. Using rural slaves to increase the population of nearby cities can also be useful to speed up urbanization, as most of the slaves will eventually promote and begin producing other resources such as manpower, research points, and trade routes that may be more useful. Note that moving the last pop away from a territory will decolonize the territory and make it unowned.

In addition, manually moving pops is particularly useful for quickly shifting the demographics of a territory to have a dominant integrated culture and state religion to meet the requirements for colonization more quickly than assimilation and conversion would normally allow. Note that with sufficient gold, a slave pop (or a tribesmen pop, for tribal countries) can be moved an arbitrarily large distance between connected territories by moving the pop to the edge of the province, using the adjacency condition to move the pop into an adjacent territory in the next territory, and continuing until the pop has been moved to its desired location. This means that even territories far away from a significant source of integrated culture and state religion pops can have pops moved there to begin colonization, if the country is willing to spend enough gold.

Enslavement

主条目：Enslavement

When an army with a general occupies territories of an enemy nation, some of the pops in the territory may be enslaved, forcibly demoted to slave status (but retaining their culture and religion) and sent back to the homeland as a spoil of war. The number of pops that are captured is a percentage of the territory's population depending on the occupying army's enslavement efficiency, and of those, around 2/3 will actually be enslaved and sent back to the homeland (with the other 1/3 of captured pops killed instead). The enslaved pops will generally be distributed according to a territory's migration attraction, preferring the capital territory (and to a lesser extent province capitals) while strongly avoiding any territories that are at or above their population capacity.

Enslavement is one of the most powerful ways to increase a country's population, besides direct conquest, if there are accessible areas that the country can easily occupy, and it is often a good idea to occupy even unimportant territories in enemy countries in order to maximize the number of pops that can be enslaved. The general concentration of enslaved pops in cities also means that they will usually eventually promote, swelling the ranks of the higher classes as well.

While sacking large cities and populous areas can be a great economic and demographic boon to the homeland, the reverse is equally true for areas that have seen their pops enslaved, making enemy occupation dangerous and potentially ruinous even if no demands are actually enforced against the country. Even the most highly populated areas will eventually be heavily or even completely ruined and depopulated as their pops are killed or carted off if they are constantly sacked, occupied, and fought over.

Colonization

主条目：Colonization

When a nearby unowned territory is colonized, one integrated culture state religion pop will be moved from the origin of colonization to the territory being colonized.

Population Capacity

Each territory has a certain population capacity, which determines how large of a population a territory's terrain and infrastructure can support. Territories have a base population capacity of 10, which is modified by a number of modifiers from terrain, technology, buildings, events, and more. Knowing which territories are good for population growth is essential in city placement and economic planning; it is almost always better to construct new cities in territories with a higher base population capacity, as larger cities are almost always richer and more productive than smaller ones, and population capacity is usually the main factor that restricts the growth of cities. Note that population capacity is a different value and modifier, though related, from food, which also services as a limitation to the population of a territory.

Some of the most important modifiers to population capacity include:

• +5 for settlements
• +22 for cities
• +30 and +10% for metropolises
• +0.25% per point of civilization value
• +10% for farmland terrain
• -10% for forest terrain
• -10% for marsh terrain
• -15% for jungle terrain
• -20% for mountains terrain
• -30% for desert terrain
• +5% if there is a nearby river
• +10% if adjacent to a major river
• +5% for coastal territories
• +5% for territories with a Warm Climate
• -15% for territories with a Arid Climate
• -20% for territories with a Frigid Climate
• -25% for territories with a Alpine Climate
• -75% if the province has run out of food and has a Critical Food Supply
• +10 in the capital territory
• +6 in province capitals
• +1 per level of port
• +10% from tribal settlements
• +4 from aqueducts
• -10% from earthworks
• +5% from a great wonder with a tier I Fertile Nation effect
• +7.5% from a great wonder with tier II Fertile Nation effect
• +10% from a great wonder with tier III Fertile Nation effect
• +15% from a great wonder with tier IV Fertile Nation effect
• +2.5% from each State Infrastructure province investment
• +25% from the City Planning national idea
• +2% from each level of Civic Advances
• +10% from the Pedagoguery invention
• +5% from the  塞琉古帝国 unique Imperial Calendar invention
• -20% for tribal countries
• +10% as a passive modifier of many deities (+12.5% if the holy site is held)
• +5% from   Heritage of Chandragupta (Maurya)
• +10% from River Plains group heritage

It is theoretically possible to raise the population capacity of any territory as high as desired by stacking bonuses from the State Infrastructure province investment and Civic Advances, but the small percentage increases means that this is prohibitively expensive. However, as in cities and metropolises every 10 pops unlocks a new building slot, it is possible to stack city population capacity arbitrarily high (given enough time) by building aqueducts if the total of the percentage modifiers is at least 150% - possible with a reasonable number of State Infrastructure province investments by the midgame - which will make each aqueduct give +10 population capacity, enough to create another building slot to build another aqueduct once the population capacity has been filled. It is usually strongest to do this in the capital, which has a number of bonuses that makes each individual pop even more productive.

If a territory exceeds its population capacity, it will get one instance of the Overpopulation modifier for every pop over the population capacity, giving:

• -3 Migration Attraction
• -4% Local Population Happiness
• +1 Migration Speed
• -0.04% Local Population Growth

The population of territory with any significant amount of overpopulation will therefore usually quickly fall back down through migration and population death, while population growth from natural growth, immigration, and enslavement will be quickly stalled, providing an effective soft cap on the population that a territory can sustainably have. It is generally rarely worth having an overpopulated territory, unless the territory only needs to go slightly over the population capacity to meet the threshold to produce another trade good.

Pop Ratio

Every territory has a desired optimal ratio for each pop class that the population of the territory will slowly drift towards, determined by the sum of all pop ratio modifiers ( Noble Desired Ratio, Citizen Desired Ratio, Freeman Desired Ratio, Tribesman Desired Ratio, and Slave Desired Ratio) that apply to the territory and its owner. Some modifiers are local and apply only to a single territory (Local Desired Ratio), some apply to all territories in a country (National Desired Ratio), and some apply to all territories with city status in a country (Desired Ratio in Cities).

Despite what it might suggest, a modifier that increases the ratio of a pop class by a certain percentage does not necessarily actually increase the optimal ratio of that pop class by that amount. Instead, the optimal ratio of each pop class is normalized by summing up all the desired ratio modifiers for that class (with a minimum desired ratio of 0) and dividing it by the total desired ratios over all 5 pop classes:

[math]\displaystyle{ \text{Optimal Ratio for Class}=\frac{\text{Desired Ratio for Class}}{\text{Desired Noble Ratio} + \text{Desired Citizen Ratio} + \text{Desired Freeman Ratio} + \text{Desired Tribesman Ratio} + \text{Desired Slave Ratio}} \cdot 100% }[/math]

For instance, in a settlement owned by a monarchy with no other modifiers, there is a +10% Local Slave Desired Ratio modifier from the territory rank and +2.5% National Freeman Desired Ratio from the government form that is applied. This gives a final desired ratio of [math]\displaystyle{ 2.5/(2.5 + 10) \cdot 100% = 20% }[/math] for freemen and a final desired ratio of [math]\displaystyle{ 10/(2.5 + 10) \cdot 100% = 80% }[/math] for slaves. One major effect of the way that the optimal ratio is calculated is that the effect of further modifiers is high when there are few desired ratio modifiers to begin with, but decreases rapidly as more and more are applied.

The rank of a territory is one of the main factors that affect the desired class ratios of a territory:

Settlements	Cities	Metropolises
+10% Local Slave Desired Ratio	+15% Local Noble Desired Ratio +30% Local Citizen Desired Ratio +40% Local Freeman Desired Ratio +25% Local Slave Desired Ratio	+10% Local Noble Desired Ratio +30% Local Citizen Desired Ratio +30% Local Freeman Desired Ratio +15% Local Slave Desired Ratio

Each overall government form also applies further modifiers to pop ratios in each territory:

Monarchy	Republic	Tribal
+2.5% National Freeman Desired Ratio	+2.5% National Freeman Desired Ratio +5% Desired Citizen Ratio in Cities +7.5% Desired Freemen Ratio in Cities	-7% National Noble Desired Ratio +10% National Tribesmen Desired Ratio

Several buildings, particularly those in cities and metropolises, also modify the desired class ratios locally:

• +1% Local Noble Desired Ratio per Academy ( city building)
• +2% Local Noble Desired Ratio per Library ( city building)
• +6% Local Citizen Desired Ratio per Court of Law ( city building)
• +6% Local Freemen Desired Ratio per Forum ( city building)
• +6% Local Slave Desired Ratio per Mill ( city building)
• +15% Local Freemen Desired Ratio with a Barracks ( settlement building)

Certain laws and government types can also affect the desired ratio of pop classes across all territories with city status in a country, including:

• +10% Desired Freemen Ratio in Cities for an Aristocratic Monarchy
• +10% Desired Freemen Ratio in Cities for a Stratocratic Monarchy
• +15% Desired Slaves Ratio in Cities with the Tyrant Kings Monarchy law
• +10% Desired Citizen Ratio in Cities with the Relax Citizenship Status Monarchy law
• +10% Desired Freemen Ratio in Cities with the Courts for Landowners Monarchy law
• +15% Desired Slaves Ratio in Cities with the Slave Treatment Sanctions Republic law
• +10% Desired Citizen Ratio in Cities with the Cultural Primacy Republic law
• +10% Desired Freemen Ratio in Cities with the Manumittance Policy Republic law
• +15% Desired Slaves Ratio in Cities with the Lex Ogulnia   Roman Republic law
• +10% Desired Citizen Ratio in Cities with the Lex Aelia Et Fufia   Roman Republic law
• +10% Desired Freemen Ratio in Cities with the Lex Domitia de Sacerdotiis   Roman Republic law
• +20% Desired Freemen Ratio in Cities with the Rights of Man Tribal law
• +20% Desired Citizen Ratio in Cities with the Rights of Birth Tribal law

A number of other local modifiers can also change the pop ratios of a territory.

The overall effect of these modifiers is that nobles and citizens are found almost exclusively in cities and metropolises, as well as to a lesser extent in capitals (even those that are settlements), while settlements will be dominated by slaves and either freemen for republics and monarchies or tribesmen for tribal countries. Increasing the movement and migration of pops from settlements to cities will therefore result in an overall higher proportion of nobles and citizens in the country, which is generally recommended as nobles and citizens are the only source of research points which is needed to keep up in technology.

Promotion and Demotion

The pop class structure of territories will change over time to approach the optimal ratio through promotion and demotion. Every territory will have one pop promoting and one pop demoting at a time until the actual pop class ratio converges with the optimal ratios for each class in that territory, as long as there are pops that are eligible to be promoted or demoted. Pops cannot promote or demote if they are currently assimilating or converting; as well, pops cannot promote past the assigned civic rights of its culture, which is particularly important when trying to promote pops into citizens and nobles. Slave promotion (to freemen) can be blocked on a territory-specific basis using the Slave Promotion Allowed toggle in the territory population interface at the cost of -24% slave happiness, which can be useful to prop up tax income and increase the amount of trade goods produced, though fewer pops of other classes will mean less manpower and particularly research points and trade routes.

As with other pop activities, promotion and demotion of pops gain progress each month, with the exact amount of progress determined by the Pop Promotion Speed and Pop Demotion Speed modifiers, respectively. Once progress reaches 100%, the pop will promote by one level or demote by one level and another pop will begin to promote or demote, if there are any other pops that can do so. Note that pops will only ever promote or demote by one level regardless of how far the territory's current pop classes are from the optimal ratio - for instance, a slave will need to promote three times before it can become a noble, even if there are currently no nobles in the territory. As an exception, while tribesmen while promote to freemen and demote to slaves as expected, freemen will demote directly down to slave status rather than passing through tribesmen first. Similarly, slaves can promote to both freemen or tribesmen, depending on the current situation.

The base promotion and demotion speed depends on the original class of the pop (not the class it is promoting/demoting to), with nobles and tribesmen particularly slow to promote or demote:

Promotion speed

• Citizen Promoting: +3
• Freeman Promoting: +4
• Tribesman Promoting: +1
• Slave Promoting: +4

Demotion speed

• Noble Demoting: +1
• Citizen Demoting: +2
• Freeman Demoting: +5
• Tribesman Demoting: +1

Promotion speed is then affected by many other modifiers, including:

• +2.5% for each pop in the territory
• +2.5% for each trade route in the province (including both import and export routes)
• +2.5% for each outgoing road
• -10% for each point of unrest
• -25% in settlements
• +10% in metropolises
• +25% in the capital
• +10% in province capitals
• +10% for ports
• +25% with a capital surplus of livestock
• +10% with the Granted Manumission invention (requires Civic Advances 10)
• +15% per governor finesse plus a base of +15% with the Social Mobility governor policy
• +10% with the Granted Manumission invention (requires Civic Advances 10)
• +20% with the Gradated Citizenship invention (requires Civic Advances 17)
• +25% for Federated Tribes
• +0.025 for each point of positive centralization
• +6 with the Military Settlement Policy Republic law
• +6 with the Lex Servilia Glaucia   Roman Republic law
• +2 with the Sedentary Bureaucracy Tribal law
• +25% if the country is Jain
• +10% with   Helot Heritage (Messenia)
• +10% with Bosporan Heritage
• -10% with   Elean Heritage (Elea)
• +0.20% for each point of revanchism

Similarly, modifiers to demotion speed include:

• +2.5% for each pop in the territory
• +1% for each outgoing road
• +10% for each point of unrest
• +33% if the food supply of the province reaches 0 and population is dying of starvation
• +10% if the territory is currently occupied or under siege
• +10% if the territory was recently plundered by pirates
• +5% if the dominant religion is not the state religion
• +15% per governor finesse plus a base of +15% with the Social Mobility governor policy
• +10% per governor finesse plus a base of +10% with the Harsh Treatment governor policy
• +6 with the Relocation Policy Republic law
• +6 with the Lex Papia de Peregrinis   Roman Republic law

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