Silent and Greatest Gen. The Lost Generation that fought in WWI was absent in Europe due to death and honestly got pretty degenerate in the roaring 20s. That and the depression I think might have fucked up both... but there have been similar cataclysms to the world wars and depression in the past. The plague wiped two thirds of the European population at one point.

There's a lot of variables at play here. But every little shitty thing has helped.