The total casualties in World War I are just under 37.5 million people, including soldiers killed, wounded, prisoners and missing in action. This war is among the bloodiest in recorded history.
There were about 65 million total mobilized forces on both sides of World War I. To put casualty number in perspective, an estimated 57.5 percent of total mobilized forces were considered casualties by the end of the war. It was the third-deadliest war in United States history, trailing behind only World War II and the American Civil War. The country with most casualties was Russia, with 9.1 million killed, wounded or missing in action.