Which event directly led to the end of World War II involving the use of atomic weapons?

The use of atomic bombs dropped on Nagasaki and Hiroshima in August 1945 is a pivotal event that directly contributed to the end of World War II. These bombings resulted in unprecedented destruction and loss of life, compelling Japan to surrender unconditionally. The day after the bomb was dropped on Hiroshima, Japan faced the reality of its predicament, which was further compounded by the Soviet Union declaring war on Japan shortly thereafter. This combination of overwhelming military pressure and the devastating impact of the atomic bombings led to Japan announcing its surrender on August 15, 1945, officially bringing World War II to a close.

Other events listed, such as the Battle of Stalingrad and the signing of the Treaty of Versailles, either occurred much earlier in the timeline of World War II or pertained to different conflicts altogether, and thus did not directly lead to the end of this global war. Similarly, the formation of NATO is related to post-war geopolitics rather than the conclusion of World War II.