Are you being serious when you say America has a relatively monolithic culture? Relative to whom?

Yes, by and large Americans have the same basic values and interests. The most popular entertainment figures, sports, musicians, and other cultural elements come from a very wide range of backgrounds. Values like individual freedom or the importance of voting are fairly universal among Americans.

As I said, this is easy to observe from abroad, where there is no space to differentiate between black Americans and white Americans. They’re all just Americans and they mostly act the same way.