World War Two (1939-1945)
World War II, or the Second World War, was a global war, the joining of what had initially been two separate conflicts.
The first conflict began in Asia in 1937 as the Second Sino-Japanese War; the other began in Europe in 1939 with the German invasion of Poland. This global conflict split the majority of the world's nations into two opposing military alliances: the Allies and the Axis Powers.
Spanning much of the globe, World War II resulted in the death of over 60 million people, making it the deadliest conflict in human history.
Here is a Crash Course video detailing the key events of the war: