Territory
As tribes grow larger and hit a certain population (lets say 60), they are given the ability to start placing outpost totems. They will be given 1 outpost for every 20 or so members after 60, so a tribe with 100 members would get 2 outposts. The logic behind the limit is, by expanding the land tribes would be spread thin if they didn't have the members to support it. These outpost would not have safe zones and would be completely free to attack.
In each zone there would be a (or more then one) spot to place the outpost totem. By placing an outpost, it would create an "Area of influence" territory in the zone, owned by this tribe. Anything (other small tribes) living in the area would now be under "rule" of this larger tribe. By "rule" I mean laws, religion, currency and possible tax set by the ruling tribe.
I haven't quite figured out how protection will work because of safe zones currently in game. Ideally it would be up to the controlling tribe to protect those they rule. realistically, we all know that wouldn't work. This is up for suggestions.
Back to attacking outposts. As I stated before, outpost are freely attack-able but the real fun comes from being attacked by another large tribe. If a outpost is conquered by a random small tribe it would merely be destroyed and the area of influence would recede back to public land. This would be a good reason to keep the tribes under your rule happy.
If another large tribe is close enough to the zone (with either their main tribe or an outpost) and they attack and conquered the outpost, they would (if they have a free totem to place) have the option to take over the zone, thus expanding their influence.
Political
Ruling tribes will be able to create laws, import/export contracts (with other ruling tribes), Alliances, declare War and peace treaties.
Type of governments: Ruling tribes could have the option to create their type of government. From democracy, where players vote for their leader, to a monarchy where there is one ruler until he decides to step down.
Laws would control the conduct of the population under rule, (how much control needs to be discussed). It could regulate what resources could be harvest or how much. breaking these rules could turn players into criminals that make them freely attackable
Import/Export: This would create a contract that ruling tribes would have with other tribes for the exchange of resources (IE: from 5000 stone or 1 large log)
Alliances/War declarations and Peace treaties:Pretty self explanatory. It would come with timers to keep the same problems DF had with wardecking on the fly.
This is what I have so far, feel free to contribute.