The British did not suddenly and instantaneously turn American in 1776, they had to already be culturally American for things to have wound up there.

What's more, the British didn't leave Britain so they could go be British overseas necessarily, but so they could go do un-British things, it could be argued.

On top of that, 250 years is both a very short time, but also a very long time. It's more than enough not to be hand-waved away, at least. In 250 years it went from a coastal breakaway to the sole hyperpower, slavery came and went, communism arrived and died out, the information age dawned, religion became more of a niche than a facet of everyday life... That's a lot of cultural upheaval.

Let's revisit where exactly it is that slavery went. It went into prisons, where it remains legal and used, with about a million people bound by it.

To make a long story short, in the US, you are and have always been one of two things: the exploited or the exploitor.