It's something that really started mid-XIX century, with the emergence of the concept of ethnic-based statehood in France and Prussia. The process continued una

It's something that really started mid-XIX century, with the emergence of the concept of ethnic-based statehood in France and Prussia. The process continued unabated for about 100 years, until the populations were divided "cleanly enough" in most of the continent. The end of WW2 was just the last chance for big moves in that direction, and some countries grabbed it with both hands.