Maybe just me, but I recall growing up, hearing nothing from my teachers and at home but about the similarities, the things we all share [as Americans], the things that make us brothers and sisters. Before all that the differences seemed to pale. And dammit, that was working. We were crawling out.
Then we hit the correctness wall. And diversity became the lesson. No longer did we teach we're not different, now we teach we are different. Heck, the differences are throw in our faces daily. The similariites, not so much anymore.
Same thing with political parties.