Historical evidence to promote or debunk Multiculturalism?

People say America is a melting pot, but when people to America from other countries, they typically moved to areas that had recent immigrants like them. That's why we have Chinatown for example. Even today, you can look at any major metropolitan area and find that people of tend to live in different areas according to race.

People tend to want to be around other people like them.

Multiculturalism has always existed, so there's nothing to debunk. All empires were multicultural by definition and most nations have always had minority cultures and ethnicities within their borders

Promote - The Roman Empire.

Debunk - everything else.