It really adds little to the game.
Logically it is a silly idea because to conquer any sufficiently size planet would require vast armies.
How would it work in reality?
Whomever had space superiority would win. Game mechanics wise, depending on empire type, civics, traits, and even factions, would determine if a planet surrenders and THEN you land occupying armies which would be used to maintain control until sufficient time passes you have full integrated the population.
How I would do it is....
- Achieve space superiority
- Order fleet to bombard
- Check for surrender
- Create a surrender value (some weights to give ideas)
- Surrendering to exterminator/devourer/assimilator +250
- Xenophobe or Militarist +50 Fanatic of either +125
- Fanatic Spiritualist when invaded by Spiritualist or Fanatic Spiritualist +50 / +125
- Fanatic Pacifist -200
- Post Surrender
- Spawn factions two or more factions
- Default faction #1 adopts invaders ethics (in effect, they accept the outcome unconditionally)
- Default faction #2 is resistance scored similar to prior to surrender
- More population will be here when scored higher (faced with someone who wants to eat you isn't fun)
- Any other factions created as resistance, Gestalt only get first two, spin off based on ethics opposition
- Assign garrison, here is where all those armies you sent come in.
- Each assigned army reduces chance for uprising by opposed factions
- Each assigned army works to integrate all faction members to faction #1
- Original empire can land armies to remove invader armies; even if they cannot control system!
The idea is that with space superiority and faced with being bombed into oblivion nearly any intelligent specie will choose surrender. How much devastation they are willing to accept before surrender needs to be determined. Then armies can be landed and occupy the world and covert/consume it. Landing armies to liberate a world could be an espionage activity or just brute force a transports to the planet even if you lose the fleet that got them there.