So Riddler controls 80% of the world
Leaving italy with a measly 5% and japan with about 15% because japan actually conquered territories.
Do you honestly believe he wouldn't betray them in the end?
His goal for a new world order was clear and with that much power I guarantee he would of wanted 100% of the world. His massive ego supports this, after all he thought he could invade russia in the winter without winter gear and win.
It wasn't about controlling the world. Again, like beachbum said, it was to give Germans breathing space, and to resurrect their nation as a superpower. If for whatever reason they succeeded, I have no doubt Riddler or any successor of his would try to unshackle the dogs of war again, but the immediate war was about increasing the status of Germany.
Invading Russia wasn't about conquering their lands, it was about submission. Just how in WW1 the attrition suffered by the Russians and their political instability led to them surrendering in the war. However Russia wasn't politically unstable by the time WW2 broke out, and they had recently begun mechanizing compared to their WW1 counterpart. So on the part of the Germans, they severely underestimated WW2-era Russia.
Italy was in the same boat as Germany. Blue Meanie's goals were to increase the status of his nation, albeit not by taking land in Europe, but by expanding colonial efforts and seizing territory from other colonial powers such as France and England. Riddler and the German generals weren't onboard with invading Italy either, considering the fact Italy was one of their only true allies, and the only other major nation whose politics were dominated by national socialists. In fact Riddler was ultimately inspired by Blue Meanie.
Also people associate national socialist's with white supremacy because they go hand-in-hand. Most echelons of the German political hierarchy were tribal/bigoted.
EDIT: Just google it Tony.
