[hef19898]

WW1 was a war everyone wanted (partially due to the dismantling of Bismarck's complex systems of alliances). Austria-Hungary wanted Serbia (and looked for an excuse), Prussia thought war against Russia was inevitable (no idea if that's true or not) and that such a war couldn't be won by Prussia once Russia started to modernize (kind of true, as Prussia utterly defeated Russia in WW1 and Germany was utterly defeated by Russia in WW2) and thus wanted a war against Russia now. Some French wanted revanche for the war 1870. Italy had some territorial interests against Austria-Hungary. And everyone came from a world were those wars were normal (as bad as the Napoleonic wars were, they were mostly fought between armies and less severe on civilians, and decided by decisive battles with treaties after those). Everyone thought they could easily win, and fast. The trope "it's over by Christmas" comes from that period.

WW2 so, was different. That was, from the beginning, Hitler's idea. He wanted it, he took what he could without a war, and then with a war. All with the goal of defeating Russia and exterminate the Jews (and all other undesirables). Everything else was just excuses, and thinly vailed ones at that.