Bombs that were dropped during the war. They created firestorms that sucked oxygen from the air, and reached temperatures as high as 1,800 degrees Fahrenheit. (982.2 Celsius) People who did not die from the fire itself, suffocated.

See: Dresden.

The typical World War II incendiary bomb was really a dispenser; it would ignite an onboard supply of magnesium or thermite, and spread the burning substance as widely as possible over its target area in an attempt to ignite everything there.