The twentieth century is called the century of war because of its unremitting disasters: two world wars, the ensuing Cold War that developed between East and West, and countless regional conflicts. As symbolized by Hiroshima, Nagasaki, and Auschwitz, these wars were marked by the targeting of non-combatants-defenseless children and adults-for slaughter, a phenomenon that left deep scars on the hearts of people around the world.

Against this background, the swift development of industry and technology during the 20th century spurred the invention of many new weapons. World War I in particular, which began in 1914, transformed the conditions under which war was fought. Many fell piteously to the airplane, the tank, and poison gas. In waging the war, professional soldiers were joined by ordinary citizens who joined armed forces through conscription or their own free will. This new kind of war embroiling whole countries required a new name: all-out war. Leaders increasingly believed that effective means of winning the war included destroying production facilities and transport systems, and killing and injuring tremendous numbers of enemy non-combatants to quash the will to fight. The indiscriminate bombing later carried out during World War II was the logical extension of this advent of all-out war and the surge in technological development. All-out war reached a peak in the atomic bombings of Hiroshima and Nagasaki.