In the 20th century in our TL, we saw massive emigration (sometimes involuntary, in the case of ethnic Germans) of ethnic Germans (from Eastern Europe and the former Soviet Union) to Germany, of ethnic Jews (primarily from Europe, the Middle East, and North Africa) to Palestine/Israel, of ethnic Russians (from the other ex-USSR countries) to Russia (after 1991), and arguably (depending on whether or not the numbers are sufficiently large for this) of ethnic Greeks (from Turkey in 1923 and from the former Soviet Union after 1991) to Greece.
Anyway, my question here is this--which other cases of massive immigration of a diaspora (especially an ethnic diaspora) back to their homeland can there realistically be?
(Indeed, there would need to be something which would compel hundreds of thousands or--better yet--millions of people from a particular/specific diaspora to immigrate (back) to their homeland--not exactly an easy task!)
Anyway, any thoughts on this?