Basic video guide: https://www.youtube.com/watch?v=vL28KdA0AdQ

Population Classes
There are 4 classes of people for each faction. These have different names depending on the faction:
1) Upper Class (Nobles/Partricians)
2) Middle Class (Plebians/Warrior Class)
3) Lower Class (Proletarii/Commoners)
4) Foreigners

Total population and starting population reflect a ratio of the general levels of population at the time for specific regions in terms of males at fighting age. You can see the population of a region by mousing over the population number in the top left of the region panel.

Population Growth
Population growth is influenced by a variety of in-game factors. These factors can be seen my mousing over the growth/population section of each region panel (next to the growth bar). These factors vary based on population class and include:
- Base Growth: Each region's base growth is dependent on the ratio of the total population to the population of a specific class. As that class' population increases, it will get increasing negatives based on the "Penalty per 10k Population" value seen below.
- Building Modifiers: Various buildings give bonuses to specific class growth, depending on the building type. These values are halved when your faction does not have the majority culture.
- Food: Food shortages for your faction give a huge negative to population growth, while having a surplus will give a positive.
- Majority Culture: Having the majority culture in your area will increase growth, while having the minority will decrease it (opposite for foreigners)
- Public Order: As public order decreases, so does growth.
- Taxation: High taxes for your faction will decrease growth and vice versa. The amount each class is affected is based on the "Tax Rate Modifier" seen in the table below.
- Faction and Province Capitals: Receive specific bonuses to growth values.
- Foreign Armies and Under Siege: The presence of a foreign army in the region will decrease growth and a settlement under siege is decreased even further.
- Looted or Razed Settlement: A very large penalty to growth results from a settlement that has been looted or razed.
- Minimum Bonus: If a certain class falls below a specific amount, it will get a bonus amount added each turn until it gets back above the minimum amount.


Foreign Population Mechanic
The foreigner population will impact your regions in the following manner:
1.) When you conquer a region, all it's population will be converted to Foreigners and you will have to build your citizen populations up from scratch in the region. If you have majority culture in that province, you will get half the population back rather than all foreigners.
2.) If the total foreigner population of your faction gets above 50% then it will cause public order penalty in all your regions. The greater the total % of foreigners in the faction the worse the public order will be.
3.) The % of foreigners in any given region will determine the level of administrative control over the region represented by a modifier to subsistence income. There are 4 stages of this to represent different types of regions: Heartland, Provincial, Colonial, Subject. At the start of a game most regions will have very small foreign populations.

Economic Effects
Population and class ratios will also impact the economy and public order:
- There is an ideal class % with the current default % set to: Noble = 5%, Middle = 15%, Low = 80%.
- The noble's % determines the management of the rural areas and gives a buff or debuff to agriculture income depending on if it is higher or lower than the ideal %.
- The middle class % determines the cultural, industrial and commercial buff or debuff.
- There is no current effect associated with the lower class ratio as it will indirectly contribute to the other 2 classes.[/source]Immigration
[source]Regions are split into one of 4 region types:
1) Faction capital
2) Province capital
3) Minor region
4) Frontier region (bordering any other faction's region)

Different influencers then make different region types more desirable:
1) Food shortage - Sends populations of all classes to minor regions.
2) Treasury - A large faction treasury draws all population classes to the faciton and province capitals. Losing money sends them to minor regions.
3) War - When at war, population classes will move away from frontier regions.
4) Sea trade route raided - Raiding sea trade routes sends population to minor regions.
5) Faction - Different factions can have more likelihood to be ruralised or urban.
6) Tax level - Population classes move to frontier regions when the tax rate is higher.
7) Not researching - Will result in people leaving capitols and going to minor regions.
8) Number of allies - Reduces penalty in frontier regions.
9) Class ratios - The faction will have an ideal population class ration if the regions pop ratio is different to the ideal then it will get a bonus or malus to bring it into line with the ideal base ratio. This is a multiplier applied to all other immigration influences and as such should have the largest impact on immigration movements in most cases.
10) Foreign army present, Under Siege and/or Battles fought: All populations will want to leave.

How Migration Movements Work
Each region gets a migration attractiveness/desirability rating. These are then compared against all the neighbouring regions owned by the faction. If the neighbour region is more desirable, then it will get a boost to its population and the less desirable region will lose population. People can only migrate to an adjacent region. This means that island regions will only have inter-island migration.

Mercenaries and AOR Troops
- Mercenaries and AOR troops work a bit differently to how other units are recruited. These units are broken up into multiple cultural groups depending on the culture of the unit.
- If a faction recruits a Mercenary or AOR unit from their culture group, the faction will use the population class of that unit (1-3). However, if that unit is not from the faction's culture group, it will use population from the foreign class (4).[/source]Replenishment
[source]- On capturing a settlement, replenishment in that region will be disabled for that turn as there are no citizens in the region to recruit.
- In all other circumstances, the replenishment of units will draw from the appropriate population class.
- If there are not enough people of a certain class in the region to fill even one of your units, then the army will not be able to replenish and you will be forced to return to a better populated region.