I’m not familiar with the history of the migrations to the USA of the 19th and early 20th centuries beyond a quick look at Wikipedia, but from that, it looks like it pretty much did solve itself.
Weren’t severe restrictions on immigration, practically closed borders, instituted during the early 1900s?
It depends a bit on ethnicity. Quotas were in place that favored Northern and Western Europeans over Eastern and Southern (Mediterranean) Europeans. And anyone from Europe was favored over Japanese or Chinese—thus things like the Chinese Exclusion Act of 1880.
Those favored ethnicities were also those closest to the existing elites’ desired American culture, which kinda makes the point: they felt the more dissimilar ethnicities couldn’t be absorbed at their existing immigration rate.
Weren’t severe restrictions on immigration, practically closed borders, instituted during the early 1900s?
It depends a bit on ethnicity. Quotas were in place that favored Northern and Western Europeans over Eastern and Southern (Mediterranean) Europeans. And anyone from Europe was favored over Japanese or Chinese—thus things like the Chinese Exclusion Act of 1880.
Those favored ethnicities were also those closest to the existing elites’ desired American culture, which kinda makes the point: they felt the more dissimilar ethnicities couldn’t be absorbed at their existing immigration rate.