[friend_and_foe]

The US has been the top performing economy for quite a while, yet only became truly multicultural about 50 years ago. Before that it was all European immigrants, assimilating to white american culture, and the native black people and some natives from the previous era scattered around. You had some cross border cultural transfer along the southern border and carribean, that's it. The amount of multiculturalism the US had until the mid to late 70s was about what you'd expect anywhere else in the world with land borders.

So we can say, the multiculturalism is not the cause of the wealth. The truth is, the causes of the wealth are the sizeable population, regardless of origin, and the vast natural resources it controls. The US is a westphalian state, run like a business. The European nations once were nation states, but have also adopted this model. It works, if your goal is economic output, and unfortunately your goal must be economic output because otherwise you can't compete militarily with a rival who's goal is economic output and you'll get subsumed.

[caeril]

It's also important to consider that the US, prior to the modern era, was a "melting pot" of a somewhat select group of immigrants. We routinely turned away handicapped, poor, sick, mentally deficient, or otherwise "unfit" potential citizens.

The "New Colossus" that adorns the Statue of Liberty is a fun little poem, but it does not in any way reflect the actual policies of the United States for much of its early and middle existence. We were a country that was happy to import wealthy people, scientists, conscientious hard workers, etc, while keeping the riffraff out.