Is it possible to wipe out other clans by either decimating them or seizing all their lands?

Similarly, can you collapse other tribes?

If you hurt a clan long enough, they will pick up their things and leave to recolonize away from you. Continue to go at their throat, and they will eventually leave Dragon Pass alltogether. Takes a long time, though, and it's not really interesting after their first exodus (where you get their lands), except if you REALLY hate their guts.

Tribes? No idea. I never saw a tribe destroyed in my games (but I almost never took part in tribal warfare)

Got'cha. Win round one, they go away; win round two, they go away long time.
Having rolled a war clan that is gonna be all about worshiping war gods and getting those war blessings, effectively relying on raids to grow and maintain ample stockpiles and herds, I need feuding neighbors near my clan to prey upon. If I get one of them to pack up and move away, I'm not bound to pursue them unless I have noone near me left to fight -- and I don't intend to fight everyone near me, I doubt I can form a tribe that way. But although I look forward to annihilating my first enemy clan, I don't like the prospect of having to mount raids on far-flung settlements which I expect will take seasons for my forces to reach.

This has brought up another query for me to pose, if this is alright in this kind of thread:
What exactly changes when you seize a neighboring clan's land, whether partially or wholly? Having difficulty wrapping my mind around it since some clans, albeit marked N(ear), don't actually seem to border my lands.
So how does this work exactly? Does it simply add to my lands abstractly, making them harder to patrol but giving me more land to hunt/sow/feed herds on, just as it differs when choosing how much land we got at the start?
Lemme know if I show make a separate question thread out of this, since I know I can only mark one post as the answer. Which I will do after I give other people some time to pitch in their 2 cents.

Nah, it's alright to jumble gameplay questions into the same thread. This, mostly. You get more lands to hunt, herd, and plow. Mostly hunt, as you will probably have to let a lot of it go wild, unless your population is freakishly large. It's more difficult to defend, but you will have some nice lands to give to your people if some families want to start their own village, for example. There could be other effects, but I don't remember them right now. So nothing stellar (you don't have to expand to win), but it can be nice if your population starts to grow beyond control.

Note that you can see the borders of your clan on the map, with one key (don't remember which one, sorry). It's really useful to see who is next to whom, and to explore your own tula in search of secrets, bandits and treasures.

And yes, waging war against a faraway clan is a hassle. I usually don't try to destroy enemy clans, unless I REALLY hate them. We're all orlanthi, after all, and even enemies can become friends in the long run. And I need someone to raid : I wouldn't want my warriors to get bored and do something stupid, would I? ;)

The most important advice for this game : Play as an orlanthi barbarian chieftain would, and you should be OK. Or at least, you'll enjoy the ride to hell :)

Near simply means, well, near. Close by. As opposed to Neighboring, which does border.