Well, WWI wasn’t a war of ideologies like WWII. I’ve never understood why anybody on either side bothered to fight. Jingoism, religion (both sides prayed to the same god for victory), a lack of understanding of the horrors of war, I mean who’d want to fight in the trenches knowing about gas attacks, the mud, lice, cold, gangrene etc.? We can thank better education and news media for war losing its popularity in every developed country except the US today. And back then in the English-speaking world, it was considered noble to die for your country. Today, the idea of fighting a war is to make the other guy die for his.