I agree. I have thought about this for a long time. I tried to identify where we get this human trait to create tribes(us) vs other tribes(them). But i keep thinking that in the beginning we needed that trait to survive. Communal efforts were needed to eat, stay warm, protection from predators ect. But that has morphed into "sorting into groups", "political identifiers" !!!
Religion has played a major role in this. Now science is taking over and we have new battle grounds.
But the basic tendencies remain. US VS THEM!
This is why i don't call myself a democrat or republican, black or white, irish or english ect.