as topic, can i launch my raid until someday they will fall or been tear apart??

Sort of, but this will not help you unify the tribes into a kingdom. Nor is it very easy.

well, i tried so long time, and the enemy tula wont disappear >_< btw, another question, how to expand my own tula land??

Pretty much the same answer. It is not easy, and it is not going to help you unify the tribes into a kingdom.

hmm, well, thanks for you answer ya~~

ya, agree with that, i think that why i cant totally defeat them~~ >_<

You don't have to do that: if you keep raiding them, over the course of several years, and keep destroying them and preventing them from growing, and killing off their warriors, they'll eventually start, firstly, coming to you for peace. If that doesn't work, they'll generally try to recruit some warriors from nearby, typically bandits, but if the keep being weakened by you after this occurs several times, and their clan begins to fall apart, they may move to another area of Dragon Pass, or disperse entirely. Either way, you'll gain a large amount of land suddenly, which you may well not be ready for. Let some of it go wild, and convert it to fields/pastures only as you need it.

Note I'm not saying that's the easiest method, but it's possible. I ended up with each thing happening to one clan in my current game, which is on easy difficulty, after I took about a third of their clan as thralls through 'take captives'.

Yeah, I've done that before, but I wasn't sure if you actually gained their tula land and I didn't want to give him/her false info.

Just note that if you grow too big, your clan will split in half. Have had it happen couple of times. I've driven off few clans over course of my games but never managed to destroy/disperse any. They always moved into other parts of Dragons Pass. Also while I can't be 100% sure but I think you need to be neighbours in order to take land (all the clans I've taken land from have been my neighbors).

I think I already drove a clan from Dragon Pass entirely (though I may be mistaken : It' was a few years ago). It took some dedication (as in "hitting them constantly for several years"), though

I always expand my tula by invading the ducks. I make them give me tribute to begin with, but otherwise I'm kind to them and send them gifts. I wait until my clan is powerful and land is getting scarce, then I launch a raid and seize their land. They get driven off to somewhere else in Dragon Pass, but the Beastfolk don't get angry enough to launch an apocalypse.

I've never tried to destroy a clan - there doesn't seem much point.