So, we can all agree that the First World War was bad. Seventeen Million people were killed, and Twenty Million were left wounded. The world was introduced to new forms of killing with the advent of industrialized war, and the worlds map was radically altered forever. Atop this, Spanish Flu came in and started killing people in their millions.
Your challenge, if you accept, with a PoD range from 1914-1919, is how, realistically, could the First World War have gone worse?