LogFAQs > #965298139

The Imperium of Man in Warhammer 40k is essentially space Nazi Germany.

As the lore developed (gradually, over decades) the iconography remained but the Imperium was gradually presented as less obviously evil (and it was always presented as the lesser of various evils). This makes it easier for people to latch onto.

Additionally, wargaming has always been very, very white male dominated. It makes a video game convention look like the UN. This has for the longest time been reflected in the lore. Space Marines, even now, are almost exclusively white men.

On a final note, Warhammer is very popular in countries with large white nationalist movements. I don't know which came first, its a bit of a chicken egg situation.