According to wikipedia, there were 37 million casualties, 16 million died in the war, and 21 million were wounded, and that's including civilians. This is about accurate considering the ongoing and never ending battles going on at the border of France and Germany. It wasn't until America entered the war when the allies started winning over the Germans. Many more died in World War 2, however, which probably had the most casualties in any war in Human history. Hope this helped!