The use of poison gas in World War I was a major military innovation. The gases ranged from disabling chemicals, such as tear gas and the severe mustard gas, to lethal agents like phosgene and chlorine. This chemical warfare was a major component of the first global war and first total war of the 20th century. The killing capacity of gas, however, was limited — only 4% of combat deaths were due to gas. Because it was possible to develop effective countermeasures against gas attacks, it was unlike most other weapons of the period. In the later stages of the war, as the use of gas increased, its overall effectiveness diminished. This widespread use of these agents of chemical warfare, and wartime advances in the composition of high explosives, gave rise to an occasionally expressed view of World War I as "the chemists' war".