The Second World War or World War II is a global military conflict, the joining of what is initially two separate conflicts.

The first had begun in Asia in 1937 as the Second Sino-Japanese War; the other begins in Europe in 1939 with the German invasion of Poland.This global conflict, which splits the majority of the world's nations into opposing military alliances—the Allies and the Axis powers—involves the mobilization of over 100 million military personnel, making it the most widespread war in history, and places the participants in a state of "total war", erasing the distinction between civil and military resources.

This results in the complete activation of a nation's economic, industrial, and scientific capabilities for the purposes of the war effort.

Over 70 million people, the majority of them civilians, are killed, making it the deadliest conflict in human history.

The financial cost of the war is estimated at about a trillion 1944 U.S. dollars worldwide, making it the most costly war in capital as well as lives.The Allies are victorious, and, as a result, the Soviet Union and the United States emerge as the world's leading superpowers.

This sets the stage for the Cold War, which is to last for the next 45 years.

The United Nations will be formed in the hope of preventing another such conflict.

The self determination spawned by the war will accelerate decolonization movements in Asia and Africa, while Europe itself begins moving toward integration.