What is the difference between Palestine and the USA?

One of the arguments of the anti-Israeli propaganda is that "there is no such thing as a Palestinian people." And this is an "invention."
I asked: Isn't this something that is correct to say about every nation, nationality, and state? After all, all of them as national groups exist only in the common human imagination? And what's the difference if it's 70 years old or 2,000?
That is: What exactly is the United States? A collection of European immigrants (predators). Can Americans be denied the right to their land because "there is no such thing with Americans"?!
You did not present this popular argument, and in any case I am addressing you as a person with an excellent ability to analyze concepts and arguments.
Do you see the difference between Palestine and the United States in this respect?
(I'm not talking about Israel, since G-d made us his people, then the people of Israel have a different meaning than the other random nations)