I suspect most of you will say WWII as it had greater causalties, especially civilian causalties, and Im sure some will bring up the atomic bombings and fire bombings which are fair arguments. But I'm going to have to go with The Great War WWI. Simple. It was so damn pointless. The war started for practically no reason other than countries not liking each other. There was no clear goal for either side during the fighting, and absolutely nothing was accomplished other than laying the ground work for another War.
Thanks I didn't find the right solution from the Internet.