World War II (often abbreviated WWII or WW2), also known as Second World War, was a global war that lasted from 1939 to 1945. The majority of world's countries formed two military alliances: the Allies and the Axis. World War II was the deadliest military conflict in the human history, marked by 70 to 90 million fatalities.
World War II changed the political alignment and social structure of the globe. The United Nations (UN) was established to foster International co-operation and prevent future conflicts.