I assume you are referring to WWII - it is a strong assertion to claim that was a xenophobic war. The Nazis were xenophobic, but one suspects their driving motivations for actually doing something about it were economic. They were expanding because they famously thought they needed more space and resources, and the German economy prior to the war was famously horrible and probably the major contributing factor to the Nazi movement gaining any traction at all.
In fact, I'll assert based on a hunch that aggressive wars powered by xenophobia are vanishingly rare. "[color] people are bad" is a good propaganda slogan for the troops, but nobody is going to stump up the funds to actually deploy them if there isn't some sort of economic justification.