One of the new major features of the new Total War game named Attila, which comes out on 17th, February this years going to be the migration feature of the different playable tribes.
At the very beginning of the grand campaign some of the factions won’t even have a single settlement, they are going to try to find home for themselves, while raiding and looting all other settlements.
If you are looking to control one of those nomadic tribes you must know that while you are migrating you can also set up some new cool improvements (new tents to unlock new troops, or get some other bonuses). There is also a new feature to camp, which immobilize your tribe for at least a turn. While you are camping you receive more of some of the bonuses, for instance army integrity, replenishment and increased population growth per turn.
If you occupy a settlement then you automatically change your faction from nomadic to settlement-oriented faction. You have also the ability to go back and be a nomadic tribe, but you must know that your previous tents upgrades were completely nulled.