The Herd Instinct
Our species has evolved to live most effectively in groups, and to put up walls of resentment, suspicion, and even hate against member of different groups.
Up until recently, this aspect of human civilization has been regrettable, though not potentially lethal. Now we live with a world with social media and fake news, declining educational standards, the proliferation of guns, nuclear weapons, overpopulation, impending environmental collapse, pandemics, heightened religious fanaticism, the aggregation of wealth into the hands of a few, and the decay of of morals and personal integrity.