And no matter what you think about tribal societies, we still live in tribes every day. You and your close friends are a tribe. Your family is a tribe. Forums and now social media communities are tribes. HackerNews is a tribe. Open source projects are tribes, indeed they fork over ideological differences all the time. Political parties are tribes, indeed they split and antagonize each other all the time. Nationalities are tribes. Companies are tribes. Social classes are tribes. Subcultures and "identities" are tribes.
We are not built to handle global contexts, so we collapse them into tribal ones. We do that for everything. There's always an in-group and an out-group and a hierarchy if we're talking about a cluster of people.