<P> World War II ( often abbreviated to WWII or WW2 ) , also known as the Second World War , was a global war that lasted from 1939 to 1945 , although related conflicts began earlier . It involved the vast majority of the world 's countries -- including all of the great powers -- eventually forming two opposing military alliances : the Allies and the Axis . It was the most widespread war in history , and directly involved more than 100 million people from over 30 countries . In a state of total war , the major participants threw their entire economic , industrial , and scientific capabilities behind the war effort , erasing the distinction between civilian and military resources . </P>
when did world war 2 officially start and end
1939 1945