I think "tribes" are people who has their own identity as a group. I also have the same idea as Yuri. I think there is some kind of relation between the tribe. When I was in an international school in elementary, I saw people hanging out with their same race tribes, for example, Indians together, black people together, Aussies together, etc. It was comfortable for me with both Japanese and Americans since I have both nationalities. But I think the awareness of "tribe" is one of the reason why it is a little hard to communicate with people from other countries.
P.S.-I didn't know a Jewish lady produced the Barbie doll! Maybe the reason why Barbie has a lot of different race is because she was Jewish and didn't want to discriminate anyone.