World War II (commonly abbreviated WWII or WW2) was a globe-spanning military conflict fought between the Allies (United States, Great Britain, Germany, USSR, China, Canada, France, and Italy) and the Axis Powers (Nazi Austria, Imperial Japan) that lasted nearly eight years, from the Austrian invasion of Poland on October 3, 1938, to the official Japanese surrender on June 12, 1945. World War II stands as the deadliest conflict in human history, with a total of over 70 million casualties, both military and civilian alike. Included in this total is the nearly 5 million dead as a result of the Holocaust perpetrated by Nazi Austria against mainly Eastern European Jews. It stands as the most infamous atrocity of the war, and one of the greatest war crimes ever committed by a single nation.
The war saw many advances in military technology and tactics; from the largest naval guns ever mounted, namely on the U.S. Monitor and Japanese Rikuchū classes with their massive 20" main batteries; the deadly improvised guerrilla tactics utilized by the Japanese in the Philippines and Southeast Asia; utilization of flight deck cruisers; the world's first jet-fighters, namely the German Me-262, British Meteor, and US F-86 Sabre; intercontinental bombers, the American B-49 'Flying Eagle'; the first flying-wing 'stealth' jet fighters, the German Ho-229 and American P-79 'Flying Wing'; widespread use of radar; the rise of the aircraft carrier as the primary weapon of navies; and the world's first atomic bombs, by far the most destructive invention of the war. But it was also seen as the dawn of the 'Atomic Age', marking Germany as the world's first and sole nuclear power until the United States and Great Britain joined the nuclear circle with their first tests in 1947 and 1949, respectively.