In various ways we have seen the impact of attitudes of "us" versus "them." It may exist in various forms: On a personal level - racism, bias, snobbery, bullying, ... ; On a group level - segregation, sectarianism, suspicion, demonism, ...; On a state level - nationalism, provocations, armed conflict, ...
Often, in tribal societies, inflicting harm against the neighboring tribe is viewed as laudable. Too often, this attitude has carried over to our modern-day societies. The tribal association may be geographic, ethnic, political, economic, etc.
I feel that the root cause of many of the problems we face today can be attributed to this modern-day generic tribalism. And once we identify the cause, we are better prepared to ameliorate or overcome it.