World War I casualties
The total number of military and civilian casualties in World War I were about 40 million: estimates range from 15 to 19 million deaths and about 23 million wounded military personnel, ranking it among the deadliest conflicts in human history.
History of the United Kingdom during the First World War
A second publication, "Casualties and Medical Statistics" (1931), the final volume of the "Official Medical History of the War", gives British Empire Army losses by cause of death. The total losses in combat from 1914 to 1918 were 876,084, which included 418,361 killed, 167,172 died of wounds, 113,173 died of disease or injury, 161,046 missing presumed dead and 16,332 died as a prisoner of war.