1 First get allied with someone. If you are having trouble allying, trade
with them first. Pots are ideal although Ploughs will work just as well.
2 When you have allied, go to their village and keep Getting Food from
them. The inhabitants will become more and more narked at this and
eventually they will rebel against their masters and join a random tribe.
This could be yours, a neutral tribe or even back to their original owner.