Assimilation

All minor faction villages on the map begin hostile to the major factions around them. These villages will slowly produce small roving armies that will menace great powers by attacking their units and cities. These villages, however, can be pacified and later assimilated. A pacified village ceases to produce hostile units and gives a bonus worker to the city in the same region (this does not, however, increase the city's population). Pacification can be achieved in four different ways:

Razing and Rebuilding
If attacked, the village will defend itself with whatever units it has garrisoned on the village, the number of which can be seen above the village itself. If defeated, the village is razed and will stop producing roving armies, but its ruins remain on the map. After a village has been razed, the owner of the region (if there is one) may rebuild the village by selecting it as a construction option in the city menu. When the village has been rebuilt, it is automatically pacified.

Bribery
By paying a certain amount of Dust, the village will become pacified. This only affects the village offered the bribe; bribing one village does not pacify other villages in the same region. This option requires knowledge of the Language Square technology. The cost to bribe a village varies quite a bit, but is largely dependent on the number of units garrisoned in the village and their level, with a greater amount of either making the village more expensive to bribe.

Parley
Choosing to parley with the minor faction triggers the beginning of a pacification quest. If this quest is completed, all of the villages in the region will be pacified. Quest objectives vary greatly, but common ones involve destroying a minor faction's village in a nearby region, building certain buildings or units, or paying the faction a certain amount of resources. In addition to pacification, many of the minor faction quests provide a reward of Dust or resources, and some even provide unique items or technologies otherwise impossible to research. Like bribery, parleying requires the knowledge of Language Square.

Conversion
This option is only available to the Cultists and custom factions with the "Conversion" trait. By spending influence points, the Cultists may convert a minor village to their cause. The village must be pacified or razed before the conversion can take place; villages pacified by any means can be converted to the Cultists' faith. A converted village sends a portion of the FIDS yields in surrounding squares back to the capital city, boosting the main city's FIDSI output in turn. Periodically, the villages produce one of their racial units for free. Though these troops cannot be retrofitted, they can be sold for valuable Dust or used as Mercenaries. If a converted village had previously been pacified and under the control of another major faction, that faction loses all of the benefits gained from the village upon conversion, including assimilation bonuses and extra population. Unlike pillage, conversion can be used on the villages belonging to the Empires you're currently in peace with (provided one can get an army inside their territory). This, as one may expect, has a negative influence on the relationships. Mercenary units, including those generated by the villages already assimilated, can't convert villages.

The Influence cost to convert a village is determined by a few factors; to begin with, each minor faction has a slightly different base cost to convert, ranging from 21 to 26. Then the cost increases for each additional village you convert, such that the cost to convert a village is equal to that village's base conversion cost times the number of other converted villages you control plus 1. Finally, where the village is located affects the cost as well; if the village is located either in a region you control or that is unclaimed, the price is unaffected, but if the village is in a region another empire controls, the cost increases by a factor of ~1.5, and if the village is razed - regardless of location - the cost increases by a factor of ~2.

The only way to reclaim a converted village is to raze it and rebuild it.

Although the in-game tooltip claims a converted village exploits 6 hexes around it, only the hexes from the same region can be exploited.

Note: The Necrophages and all custom factions with the Pitiless trait cannot research Language Square, and consequently may not bribe or parley with minor villages; they can only assimilate minor races by destroying and rebuilding their villages.

Assimilation
When at least one village in a region you control is pacified, the minor faction that the village belongs to can be assimilated via the empire screen. In the bottom left, there is a section for assimilated minor factions. Initially, only one minor faction can be assimilated, but two more slots can be opened by researching the Native District and Cultural Indoctrination technologies (Protectors of Auriga and Tribal Council for the Drakken). If desired, an assimilated faction can be switched out for another faction if there are no open slots remaining. Assimilating and switching races requires the expenditure of influence. The cost is based on the number of minor factions you have already assimilated. Your first minor faction costs 30 Influence, the second 100  Influence, and the third 290. Switching costs are the same depending on how many factions are assimilated, i.e. if two factions are assimilated, it costs 100 to switch either of them out.

Assimilation also provides two important benefits to the major faction: a racial unit and an assimilation bonus.

The racial unit of the assimilated faction is added to the roster of troops available for recruitment and can be upgraded and retrofitted just like the major faction's own units. If a city is located in a region that has one or more of the given faction's villages in it, then the cost to produce units of that faction is reduced by 5% for each pacified and rebuilt village in the region. This unique unit type is available so long as there is at least one of that faction's villages remaining in the empire, even if the village is razed. Upon de-assimilating a given faction, any units of that faction's design will no longer be able to be retrofit, but can still be used.

Assimilation bonuses are passive bonuses that apply across the entire empire, and becomes more powerful the more of a given minor faction's pacified villages are under your control, up to a maximum of 6. Minor factions, their units, and the assimilation bonus they provide can be found below:

Tips

 * For many of the Major Factions, the early stages of their Faction Quest require the assimilation of a minor faction.
 * Regions with multiple minor villages are prime targets for colonization, as every village provides a free worker to be used in the regional capital.
 * Every major race has gaps in its military, and some roles will always be left unfilled by its native troop types. Assimilated minor faction troops can round out an empire's army.
 * Parleying is preferable to attacking or bribing early in the game, especially in regions with multiple villages. The cost in Dust to pacify a village is significant early on, when Dust should be better saved for heroes and other uses. Attacking is also difficult in the early game, as every village is defended by multiple units and some of the base minor units are more powerful than any of the early-game troops the major factions can build. Parleying also leads to quests which can yield unique technologies, resources, and Dust. And, should a quest prove too daunting, the other options remain open. However, this tends to change later in the game, as pacification quests more frequently become demands for large quantities of rare resources with no reward aside from pacification in return, but Dust is plentiful and your units can easily outclass those in a village.
 * Try to pacify and assimilate hostile villages quickly and early on if possible, certainly soon after colonizing a region, or even doing so just before colonizing it. Hostile villages produce soldiers that will rove across your empire looking for weak targets to kill, pillaging regional buildings, and occasionally sieging cities (though rarely trying to capture them).