World War 1 or World War 2?

This war caused the United Nations to be formed

Franklin Roosevelt was president during this war

The usage of harmful gases in battle was a notable characteristic of this war

The Central Powers played a major part in this war

This war brought about the incredible story of Anne Frank

Treaty of Versailles was created after this war

Trench warfare played a big part in this war

Robert Oppenheimer created the device that caused this war to end

The US became involved in this war because of an attack on Pearl Harbor

This was the first war to involve warplanes, submarines, and tanks