World War I was one of the deadliest conflicts in human history because cs A) of the massive loss of live due to atomic weapons in the Pacific and the Holocaust in Europe. B new military technology like airplanes, machine guns, tanks, and poisonous gas made combat deadlier than ever before. improved transportation and shipping methods made getting troops and supplies from one place another easier than ever before D) improved medical technology and methods reduced the effect of disease and improved survival rates for soldiers wounded in combat.