Yeah one of the things I always try to argue with liberals is that America was basically a gigantic blank slate (except for native americans that is): diverse immigration somehow worked as there was a lot of space to fill and everything had to be built.

It wasn't really a blank slate by the time it became independent, though. The USA was very strongly founded on WASP ethics and WASP demographics. It was only a blank slate inasmuch it severed its politics from European entanglements, but it remained an Anglo-Saxon state through-and-through, and carried Anglo-Saxon ideas with it wherever it went. Every small town founded on the colonies or on the frontier was an expression of those ideas, although it did meet the Spanish, French and Indian cultural spheres as well. But almost anywhere you go in the rural and small-town US, you will see white houses, porches and lawns, because that's the world the Americans created according to their own ideas of comfort. Everywhere you go, there are town halls in the same general style, and churches for the various congregations that together stuck to US protestantism.

The "great melting pot" idea that came much later (after generations of distrust against even groups like Danes, Germans and Norwegians, not to mention suspicious types like Italians, Irishmen, Jews and various Bohunks) was an offer to some of those other groups to integrate into the Anglo-Saxon bedrock and join regular US society. And they did, because that way of life was attractive, even beyond the American dream of making it big. While there were all kinds of immigrant groups in the US by the late 19th century, much of it remained unchanged. The big cities were colourful (H.P. Lovecraft had choice words about this colour), but they were not considered the better part of America, and US thinkers were always troubled by their influence on the national character. When it came to the elite; the state apparatus, political life and universities, they firmly stuck to their leading ethos until the 1960s.

Even so, the US changed, but as long as it had a Leitkultur based on the evolution of its original ideas, the model mostly worked. Now, that's what the globalists want to "leave behind" or, more like, tear down and destroy like they are doing with pieces of US history. If they succeed, they will take the US down with it. It actually becomes more of a blank slate because there are no guiding values behind the country, and anything goes. Globalists believe self-interest and the guiding beacon of global consumption will do in place of US values like the Constitution or their traditions of independent local government, and we are seeing where this kind of thing is going.