Question

Which World War II event occurred first?

Answer 1

It would be "President Harry Truman was sworn in to office" that occurred first, since the US dropping the atomic bombs on Japan effectively ended the war after Roosevelt died. 

Answer 2

The answer: President Harry Truman was sworn into office.

Harry Truman was sworn into office as the 33rd U.S. president on April 12th in 1945, following the death of President Franklin Roosevelt. While the two atomic bombs were dropped on Hiroshima and Nagasaki three months later, on August 6 and August 9, respectively, of that same year. Inevitably, Japan announced its surrender to the Allies six days later. And the following month, the war finally ended.