World War II

World War II, often known as the Second World War and shortened as WWII or WW2, was a worldwide conflict that took place between 1939 and 1945. It entailed the overwhelming majority of the world's nations all of the great powers—forming two competing military alliances: the Allies and the Axis powers, which were formed in response to the outbreak of war. As part of a total war that directly included more than 100 million troops from more than 30 nations, the main players committed all of their economic, industrial, and scientific resources to the war effort, blurring the line between civilian and military resources. Aircraft played a significant part in the fight, allowing for the strategic bombardment of population centres as well as the only two instances in which nuclear bombs were used in combat. With 70 to 85 million deaths, World War II was by far the worst war in human history, with the vast majority of those deaths occurring among civilians. The Holocaust, genocides, famine, massacres, and illness all contributed to the deaths of hundreds of thousands of thousands of thousands of people. Following the fall of the Axis powers, Germany and Japan were occupied, and war crimes courts were convened against the leaders of the German and Japanese militaries and governments.

The invasion of Poland by Nazi Germany, led by Adolf Hitler, on September 1, 1939, is widely regarded as the official start of World War II in Europe. On 3 September, the United Kingdom and France declared war on Germany as a result of this action. During World War II, Germany and the Soviet Union partitioned Poland and defined "spheres of influence" that stretched through Finland, Romania, and the Baltic republics, according to the Molotov–Ribbentrop Pact of August 1939. From late 1939 to early 1941, Germany invaded or gained control of most of continental Europe via a series of operations and treaties, forming the Axis alliance with Italy and Japan to fight the Allies (along with other countries later on). Immediately following the beginning of campaigns in Northern Africa and East Africa and the fall of France in mid-1940, the war continued primarily between the European Axis powers and the British Empire, with fighting in the Balkans, the aerial Battle of Britain, the Blitz of Britain, and the Battle of the Atlantic among the many other campaigns that took place. German forces invaded the Soviet Union on June 22, 1941, marking the beginning of the Eastern Front, which would become the greatest land theatre of war in history.

By 1937, Japan, which aspired to be the dominant power in Asia and the Pacific, was at war with the Republic of China. With simultaneous offensives against Southeast Asia and the Central Pacific, Japan forced the United States to declare war on Japan, which was followed by a similar declaration of war by the European Axis powers against the United States. The attack on the US fleet at Pearl Harbor was the culmination of the Japanese attack on American and British territories. Japan rapidly took control of much of the western Pacific, but its gains were stopped in 1942 after losing the crucial Battle of Midway; subsequently, Germany and Italy were beaten in North Africa and the Soviet Union's Stalingrad battleground, respectively. Several major losses on the Eastern Front, as well as Allied incursions into Sicily and the Italian mainland, as well as Allied offensives in the Pacific, robbed the Axis of its momentum and pushed it into a strategic retreat on all fronts throughout the year 1943. As the Western Allies advanced into German-occupied France, the Soviet Union reclaimed its lost territory and redirected its attention on Germany and her allies. While Japan experienced setbacks in mainland Asia between 1944 and 1945, the Allies weakened the Japanese Navy and took vital islands in the western Pacific during that same period.