The total number of military and civilian casualties in World War I was about 40 million: estimates range from around 15 to 22 million deaths and about 23 million wounded military personnel, ranking it among the deadliest conflicts in human history. About two-thirds of military deaths in World War I were in battle, unlike the conflicts that took place in the 19th century when the majority of deaths were due to disease. Nevertheless, disease, including the 1918 flu pandemic and deaths while held as prisoners of war, still caused about one third of total military deaths for all belligerents.