Colonists

Summary
Colonists are an advanced economic brigade that can be recruited after unlocking the colonization skill in the economic skill tree.

Once moved into a conquered city of a different native faction, they can be settled in that city with the "Settle Colonists" button if the colonist brigade is selected in the city's units tab. This will give a large one-time boost to the city's assimilation meter, but consume the colonist brigade in the process.

"Recruit colonists from your native cities and resettle them in captured cities to give a one-time bonus towards assimilating the city to your faction. Native cities have higher morale that will prevent rebellions and make it easier to collect taxes and raise new recruits."

- In-game Description

History
The ancients would send colonies to settle in areas away from their homes for various purposes. This could be to resolve social unrest in the mother-cities, by sending troublesome segments of the population away to live elsewhere, or just reducing overpopulation in general. It could also be a means for empire-building, founding subservient colonies in strategic locations to secure access to more resources. Alternatively, colonies could be settled in existing settlements conquered from other peoples, as a means of controlling and eventually assimilating the hostile locals, as in-game.

Tactics
Colonists can be very useful, if the player has excess recruits in one or more of his native cities and wishes to speed up the assimilation of occupied cities native to other factions. With a total cost of 100 recruits and an additional up-front cost of 200 gold aside from the normal upkeep of 30 gold per week, colonists are a bit of an investment, and should not be created if the player is having trouble keeping its military brigades at full strength.

Colonists should also be kept safe from enemy attacks at all costs, meaning an area needs to have been militarily secured before the player decides to send in colonists to further pacify those areas.

Since cities with a very low population level will assimilate rather quickly on their own after the colonization skill is unlocked, colonists should usually be reserved for higher population cities that will take a while to fully assimilate.

Assimilation converts the city's native faction to your own. This is especially useful if the city in question has a native faction that is hostile to your own, which will make the city far less productive and gives it the potential to rebel if not occupied by a sufficiently large military garrison. This may also change the brigade types that can be recruited in that city, if the city's native faction is of a different faction group. If the city's native faction is friendly to yours and has access to useful types of brigades that your own faction group lacks, it can therefore be useful to not assimilate that city so you can keep using it to recruit these brigades.

Assimilating cities is a necessary step towards achieving Cultural Hegemony, if the player cares about achieving victory conditions.