But yes, a lengthy period with a unifying adversary that felt like an existential threat did a lot to unify the US
This is how you wound up with historically ethnic banks, universities, etc, etc. Black guy, pole, whatever, can't get a loan (well they can, at a "fuck you" price) from the wasp bank so they go to the lending group they know through their church or whatever. After a few years of that the guys who are doing that lending say fuggit, quit their day jobs and start a bank. Wash rinse repeat to varying extents for just about every sector business.
They'd never allow that today. The incumbents would get the enforcers to kill that before it becomes a legitimate standalone business. And the enforcers have a lot more ammo today because of past 70yr of (mostly civil) law and jurisprudence.
But any modern equivalent isn't done along racial/ethnic lines and so the useful idiots will think it's all fine and dandy and defend it out of one side of their mouth while complaining about a lack of opportunity out of the other.
Keep in mind the US government pre watergate did a lot of spying on political opponents (MLK, Malcolm X, etc). Presidents impounded funds pre Watergate at alarming rates.
We interned US citizens in camps during WW2 for being of Japanese descent. See also native Americans and the Federal govts enforcement of slavery.
You might say the govt has just grown in proportion to the container it’s held in.