England and South Africa have tiny landmasses compared to America. Even the entire UK has a tiny landmass compared to America, and it's home to at least four distinct ethnicities (English, Welsh, Scottish, and Irish).

There has been no ethnostate of comparable inhabited landmass to the US in human history.

And technology does get lost, particularly when advanced societies collapse. The Greeks had analogue computers and Greek fire, unknown in the middle ages. By WW2, we had reinvented analogue computers, but the closest we've ever gotten to reinventing Greek fire was napalm, which wasn't invented until the Vietnam war. Modern concrete is still inferior to Roman concrete. The Romans had steam engines, didn't exploit them fully, and then they were lost and reinvented 1400 years later. The Egyptians could build giant pyramids that the Romans, Greeks, Chinese, and pre-industrial Europeans could not. We could just barely build them, but the cost would be extreme.

England and South Africa have tiny landmasses compared to America. Even the entire UK has a tiny landmass compared to America, and it's home to at least four distinct ethnicities (English, Welsh, Scottish, and Irish).

There has been no ethnostate of comparable inhabited landmass to the US in human history.

And technology does get lost, particularly when advanced societies collapse. The Greeks had analogue computers and Greek fire, unknown in the middle ages. By WW2, we had reinvented analogue computers, but the closest we've ever gotten to reinventing Greek fire was napalm, which wasn't invented until the Vietnam war. Modern concrete is still inferior to Roman concrete. The Romans had steam engines, didn't exploit them fully, and then they were lost and reinvented 1400 years later.