Unrest
Unrest is generated through unhappy pops, low stability in your country, war-exhaustion, governors policies and corruption. It can also be reduced by various laws, positive stability and by assigning armies to the local governor.
The happiness of a pop depends on its culture and its religion compared to the country’s religion and culture. Different pop-types also want different civilization levels to be happy, while a tribesman want it as low as possible, the citizens want it rather high. Different laws makes different types of pops more or less happy as well. Access to different goods in the city will also make pops happier.
If a pop has less than 50% happiness, they will contribute to the unrest of the province.
Impact
There are two impacts, the first is the reduction of commerce, tax, manpower and research from the city. The other is when it reaches the threshold of 10 unrest, you can no longer recruit regiments in the city, build buildings or interact with the population.
Loyalty
There are three types of loyalty:
Province Loyalty
Each province have a loyalty value to the country. If it goes down to 0, then that province is basically 100% autonomous and provide nothing to you. They will cancel all trade to other parts of your country and every city will be acting as it had at least 10 unrest.
If enough provinces are disloyal, they will either start an independence war, if the dominant culture is not your primary culture-group, or a civil war if they are of your culture-group.
There are alerts if your provinces are disloyal, or if you risk a civil war or major revolt.
Cohorts Loyalty
Each cohort in an army can become loyal to a single person. This depends on the charisma of the commander during a battle or a siege.
When a cohort is loyal to a character the country pays less maintenance for it, as the commander of the unit it is loyal to, starts paying the unit him or herself.
There is a slight drawback or two to having cohorts loyal to a character instead of the country, like for example, a cohort that is personally loyal to a character will not allow it to be transferred away from the unit in any way. Also, a character with cohorts loyal to him tend to become more disloyal over time.
Character Loyalty
Characters loyalty to the Country is one of the more interesting aspects to manage, as disloyal characters is a huge risk, as disloyal characters will refuse to abandon their armies or provinces, and if enough are disloyal they will form a block together to form a civil war.
Some forms of government, a few inventions and some ideas increase loyalty of all characters. Giving people titles and offices will increase their loyalty, but removing them decrease their loyalty. Characters of the same faction as the ruler tends to become more loyal over time, while friends and rivals of the ruler will see their loyalty go up and down as well.
When the loyalty of a character is below 33%, that character is considered disloyal.
Civil War
While a major revolt is not different from having a large nation revolt from you in other games, civil wars are dramatically different.
The threat of a Civil Wars will start as soon as either 33% of the army is controlled by a character that is disloyal OR 33% of all provinces are disloyal to the country.
During the threat of a civil war, a small timer ticks up each month, where the civil war will break out after a year. During this time you have an alert so you can see that you have a risk of it. Of course, there are alerts as soon as a single province is disloyal or a general is.
When the Civil War starts, all disloyal characters and provinces will join them.. And possible friends and families as well.
A civil war is a war-to-the-death, where provinces automatically switch owners when you occupy them, and if you lose the civil war, it is basically game over.
And always remember.. Tyranny is not a help when it comes to get loyalty.