World War II was a global military conflict which lasted from 1939 to 1945, involving most nations of the world organized into two opposing military alliances: the Allies and the Axis. It was the most comprehensive war in history, with more than 100 million military personnel mobilized. Key stakeholders dedicated his entire economic, industrial, and scientific capabilities at the service of the war effort, leaving aside the distinction between civilian and military resources. Marked by a significant number of attacks against civilians, including the Holocaust and the only time nuclear weapons were used in combat, it was the deadliest conflict in human history, resulting in over 70 million deaths.
It is generally considered the starting point of the war as the invasion of Poland by Nazi Germany on September 1, 1939, and subsequent declarations of war on Germany by France and most countries of the British Empire. Some countries were already at war at this time, such as Ethiopia and the Kingdom of Italy in the Second Italy-Ethiopian War and China and Japan in the Second Sino-Japanese War. Many who do not initially involved just sticking to the conflict in response to events such as the invasion of the Soviet Union by the Germans and the Japanese attacks on U.S. forces in the Pacific at Pearl Harbor and British maritime ultra-colonies, which resulted in declarations war on Japan by the United States, the Netherlands and Britain.
The war ended with the victory of the Allies in 1945, significantly changed the political alignment and social structure worldwide. The Soviet Union and the United States emerged as rival superpowers.
Post war is the United Nations (UN) established in 1945 to foster global cooperation and prevent future conflicts, and also approved the Universal Declaration of Human Rights in 1948, as a common standard for all member states. While the post-war division of the world was formalized by two international military alliances, the Organization of the North Atlantic Treaty (NATO) led by the United States and the Warsaw Pact led by the Soviet Union, the long period of political and military tensions from the competition between these two groups, the Cold War, would be accompanied by unprecedented arms race that would extend the next forty-six years.
Also after the war the United States occupied Japan and Korea, formerly under Japanese rule, was divided and occupied by the United States in the South and the Soviet Union in the North between 1945 and 1948, each claiming to be the legitimate government of all of Korea, which led to the War of the Koreas years later. In China, nationalist and communist forces resumed the civil war in June 1946. Communist forces were victorious and established the People's Republic of China on the mainland. In the Middle East, the Arab rejection of the Partition Plan for Palestine and the UN creation of Israel marked the escalation of the Arab-Israeli conflict. While the European colonial powers attempted to retain some or all of their colonial empires, their losses of prestige and resources during the war failed their goals, leading to the decolonization of Asia and Africa.