Word War II began in Europe on September 1, 1939, and ended on May 8, 1945. The beginning of the war was marked by the German invasion of Poland, while the end is considered to be Germany's unconditional surrender.
Most historians date the beginning of World War II in Asia to December 7/8, 1941, when Japan attacked British assets in East Asia and Pearl Harbor in the United States. The war in the Pacific ended with the Japanese announcement of the intention to surrender on August 15, 1945; the surrender took place on September 2, 1945.
Although the start of hostilities in Europe is clearly delineated by the invasion of Poland, the war in Asia is less certain, as Japan's regional hostility had been ongoing for several years with attacks on China and aggression toward smaller powers. The prevailing attitudes common at the beginning of the European war are commemorated in W.H. Auden's classic poem "September 1, 1939."