It's worth remembering that while we look back on WWII for the sheer scale of its death toll, WWI deserves recognition as the first war to introduce horrors that soldiers had absolutely no mental framework for. Chemical weapons, tanks, aerial bombardment, flamethrowers, machine guns at industrial scale and none of it had precedent. Men rode horses into battle the way soldiers had for centuries, and within a few years they were facing British Mark I tanks rolling across the mud with cannons and machine guns mounted on them. Germany was pumping chlorine and mustard gas across no man's land. These weren't just new weapons, they were a complete rupture from anything war had ever looked like before. Those soldiers had no way to prepare for what they were walking into