September 3, 1939 – Following the German invasion of Poland two days earlier, Britain declares war on Germany. France, Australia and New Zealand also declare war the same day. The Second World War has begun.
World War II (WWII or WW2), also known as The Second World War, is a global war that lasts from 1939 to 1945, although related conflicts began earlier. It involves the vast majority of the world’s nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis. It is the most widespread war in history, and directly involves more than 100 million people from over 30 countries. In a state of “total war”, the major participants throw their entire economic, industrial, and scientific capabilities behind the war effort, erasing the distinction between civilian and military resources. Marked by mass deaths of civilians, including the Holocaust (in which approximately 11 million people are killed) and the strategic bombing of industrial and population centres (in which approximately one million are killed, and which includes the atomic bombings of Hiroshima and Nagasaki), it results in an estimated 50 million to 85 million fatalities. This makes World War II the deadliest conflict in human history.