i think what caused the great number of casualties was the fact that there were many new weapons introduce such as the machine gun and flamethrower.also the weapons that were already there have been made even more deadly like artillery instead of the old fashion canons they now have much farther shooting howitzers.even the way the war was fought caused more casualties. they dug trench's and shot at each other waiting for on side to rush the other which lasted longer because both sides were at a stand still for long periods of time.