Historically, has any nation ever survived multiculturalim and mass immigration?

These two things are between the leading causes of the DEATH of great civilizations, such as the roman empire. Has ANY nation ever survived diversity, multiculturalism and mass immigration??? I DON`T THINK SO.
Update: I said HISTORICALLY. This excludes nations that currently exist like Australia, USA, etc... USA is declining while europe is collapsing so I wouldn't say these countries are being successful. The persian empire was ''multicultural'' in a different way from ours. They allowed every region to... show more I said HISTORICALLY. This excludes nations that currently exist like Australia, USA, etc... USA is declining while europe is collapsing so I wouldn't say these countries are being successful.

The persian empire was ''multicultural'' in a different way from ours. They allowed every region to keep their culture, but they NEVER MIXED CULTURES TOGHETER in the same city or place! China, Japan, India are the world's oldest nations and they have NEVER been multicultural. Other nations like the romans and the USSR have collapsed (the USSR lasted for only 70 years).
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