CE 1939 - World War II begins.

On 1 September 1939, Nazi Germany invaded Poland, marking the beginning of World War II in Europe.

This invasion precipitated declarations of war from Britain and France, leading to the European phase of the war.

The U.S. officially entered the war in 1941 after the Japanese attack on Pearl Harbor.

The war saw the mobilization of more than 70 million personnel, making it the largest conflict in human history.

It also saw the development and deployment of new and devastating weapons such as the atomic bomb.

The war in Europe ended with the defeat of Nazi Germany in May 1945, while the war in the Pacific ended with the surrender of Japan in August 1945.

The Holocaust, in which six million Jews were systematically murdered by the Nazis, is considered one of the worst atrocities in human history.

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