What event marked the official end of World War II?

The correct answer is the dropping of atomic bombs on Hiroshima and Nagasaki, as this action directly contributed to the conclusion of World War II in the Pacific theater. The bombings in August 1945 resulted in massive destruction and loss of life, which compelled Japan to surrender unconditionally. The surrender was officially announced by Emperor Hirohito on August 15, 1945, leading to the signing of the formal surrender documents on September 2, 1945, aboard the USS Missouri. This series of events firmly established the end of hostilities and marked the official conclusion of World War II.

In contrast to the other options, the Treaty of Versailles was associated with the end of World War I, not World War II. The surrender of Germany, which occurred in May 1945, officially ended the war in Europe but did not encompass the entirety of World War II, as conflict continued in the Pacific until Japan's surrender later that year. The establishment of the United Nations occurred later in 1945 and was a response to the war but did not directly signify its end.