Most of the countries in the World- if not all- are a melting pot created through invasion and war.
There's nothing that different about US except maybe that it happened later in history.
If that's even true. I mean, for instance, Byzantium fall almost half a century earlier than the discovery of America. Now Constantinopol is Istanbul and part of the Republic of Turkey.
Before it belonged to the Romans, it belonged to the Greeks who took it from the Thracians. That's history, the strong shape the World trough violence and dominating cultures, the weak whine about it.