Dysentery, typhus, and cholera were rampant, and otherwise minor injuries would prove fatal when gangrene set in. I mean, 25% of arm wounds among German soldiers were fatal. And that's not even to mention the famous influenza epidemic that broke out toward the end of the war, which killed more than three times as many people as the war itself. The main reason the war was so deadly was the combination of new technology and outdated tactics. While we may think about tanks, airplanes, and poison gas, all of which made their debut in the First World War, the two most devastating technologies were American. Machine guns and barbed wire. Attempting to march in lines toward an enemy's trench, soldiers of both sides were mowed down by machine gun fire.