The war is generally accepted to have begun on September 1st, 1939, with the invasion of Poland by Germany, and later declerations of war on Germany, led by Nazi dictator Adolf Hitler, by France and most of the countries of the British Empire and the Commonwealth, provoked by the invasion. Germany set out to establish a large empire in Europe. From 1939 to 1941, in a series of campaigns, Germany conquered or subdued much of continental Europe; amid Nazi-Soviet Agreements, the nominally neutral Soviet Union fully or partially occupied and annexed territories of its six European neighbours. Britain and the Commonwealth remained the only major force continuing the fight against the Axis in Libya and Egypt and in extensive naval warfare. In June 1941, the European Axis launched an invasion of the Soviet Union. The USSR joined the Allies and the largest land theatre of history began, which, from this moment on, would tie down the major part of the Axis military power. In December 1941, Japan, the major Asian Axis nation, which had been at war with China since 1937, and aimed to dominate Asia, attacked the United States, its possesions and European Possesions in the Pacific, quickly conquering much of the region. In response, the United States entered into military operations on the Allied side.
The Axis advance was stopped in 1942 after the defeat of Japan in a series of naval battles, led by US Admiral Chester Nimitz and after defeats of European Axis troops in North Africa and, desicevly, at Stalingrad. In 1943, with a series of German defeats in Eastern europe, the Allied invasion of Facist Italy, and American victories in the Pacific, the Axis lost the initiative and undertook strategic retreat on all fronts. In 1944, the Western Allies invaded France, in an operation codenamed Overlord led by US General Dwight D. Eisenhower while the Soviet Union regained all territorial losses and invaded Germany and its allies.
The war in Europe ended with the capture of Berlin by Soviet and Polish troops and the subsequent German uncoditional surrender to the Allies on May 8th, 1945. The Japanese Navy was defeated by the United States, and invasion of the Japanese home islands became imminent. The war in Asia ended on 15 August 1945 when the Americans dropped two Atomic Bombs on Japan.