Well I have no actual study on this but, it looks like what your homework might really wants is an opinion;so let's give them one shall we? I think the way control would be maintained is by power & intellect. Why? because those two characteristics in a being would grant them respect. This answer is also most likely because, umm hello, it's a tribe lol, means they are dirt broke hehe. So greed doesn't really get in the way like in our government. The Short Answer is This : They pick a leader, with the previously stated characteristics.... Well & obviously he needs some niggaz to back him up in a fight, if some haters try to overthrow him. =D
