How does World War 2 even make sense?

I know, "National Socialists," duh.

Let's try to look a bit beyond the painfully obvious, especially since the Germans weren't big believers in nationalism for other people, but instead were prussian supremacists with dreams of empire.

Instead, without borders, peoples with a shared culture, ruled over by their own governments and tradition, separate from other nations, why would there even be a reason to resist a few migrants with really cool tanks and uniforms?

Heck, even the propaganda of the time, even on the allied side, even among the Soviets, makes no sense without a sense of nationalism.