“Wikipedia: Amity-enmity complex

The amity-enmity complex theory was introduced by Sir Arthur Keith in his work, A New Theory of Human Evolution (1948). He posited that humans evolved as differing races, tribes, and cultures, exhibiting patriotism, morality, leadership and nationalism. Those who belong are part of the in-group, and tolerated; all others are classed as out-group, and subject to hostility…”