Maybe it's a "oce you're in, you're in" system
maybe maybe not 
im not saying town at war causes ppl to leave im saying. oh no our sovereign wont protect us from raging beasts we should go to the other kingdom where they have nice beast free towns.
Edit: also the main point of the thread is not siphoning my idea: could there be a safety stat that determines population growth instead of linear growth. heck u could even base the pop growth off of amt of essence invested or size of teh colony.