Which additional immigrant groups could have realistically come to the US in large numbers?

Futurist

Ad Honoris
May 2014
21,755
SoCal
Throughout US history, various immigrant groups came to the US in large numbers. At various points in our history, we have had large numbers of English, Irish, Germans, Italians, Jews, Japanese, Korean, Chinese, Indians, Vietnamese, Mexicans, Cubans, et cetera settle in our country. However, which additional immigrant groups could have realistically come to the US in large numbers and settled here? Also, what scenario would have been necessary in order to actually make this settlement come about?