I think we tribal humans, over the millennia, have developed an ingrained, genetic need for a common enemy, to protect our particular tribe, and it’s especially strong in the less reasoning and emotion-driven among us today.
USA now has no real, palpable common enemy as we’ve had in the past (England, natives, north-south, Germany/Japan, USSR...).
So, from our diversity, our tribes have created enemy groups to actualize this prime, driving need upon — D v R, color v white, women v men, gay v straight, atheist v Christian, MX v USA , etc.
Pick your enemy, feel that ancient battle mode energizing you, work yourself up and start engaging...
Close, but I think people survive better by alliances.
The divisions you are talking about, the tribal warfare, exist not because we lack an enemy but because we have been turned into each other’s enemies by Cultural Marxists, by subversive, by those who employ Saul Alinsky’s Rules for Radicals in using manufactured hatred as a political strategy.