The air war over Germany was an outgrowth of the German air war over much of Europe. When the Germans invaded Poland in 1939 they introduced a new dimension to warfare: the employment of massive air power. Airplanes had become a part of warfare during the first World War, but by 1918 air combat was still in its infancy. Machine guns had been placed in fighter aircraft, and aerial dogfights were part of the action. World War I planes occasionally strafed targets on the ground, but bombing missions often consisted of nothing more than pilots throwing grenades or other explosive devices out of the cockpit by hand. Airplanes were valuable as reconnaissance tools, but like tanks, aircraft had yet to become dominant factors in battle.

Priority targets for British and American pilots included aircraft plants, oil refineries, factories, transportation centers and facilities, military installations and other war-related centers. But as German defenses were worn down and allied capabilities continued to grow, dozens of German cities were bombed more or less indiscriminately. In a raid on the city of Kassel, for example, the industrial targets received only minor damage while 90% of the city's homes were hit. Toward the end of the war raids that killed thousands of individuals occurred on a regular basis.