More than eight million of the sixty-five million estimated soldiers that were mobilized for combat in the First World War were killed in action. Based on the site linked below the best estimate of the number of soldiers who returned home after duty is 56,509,979. This number doesn't include prisoners of war or those missing in action, only those that were killed. Also keep in mind that these numbers are most certainly not one hundred percent accurate due to "questionable accuracy of the recording system used and the loss or destruction of a number of official documents." These are the total numbers for the both sides of the war. Follow the link if you need more detailed information, as the website has the statistics broken down by alliance and country.