Rome did pretty good. Flawed premise
Rome was a different situation though. The tribes which came together to form Rome had a long history and their own ethnic identities and maintained those identities. America has very little identity left besides the one manufactured in the early 20th Century. Maybe regionalism can take over, but with weaponized migration, that is in doubt.
Europeans have more than a thousand year history together.
America was just the overflow apparently.
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