Age of Wonders: Planetfall

This one involves NPC dwellings. You need to raise rep to max, convince 2 of them to join with you (by quests, buying units off them and obviously not attacking them) and maintaining alliances with other players. You will then need to learn Dawn of a New Union which has an Operations called Planetary Unification Protocol. This will take some time to prime and then about 25 turns to enact AFTER being primed. This will also cause you to win the game simultaneously as earning this achievement.