Final answer:
The Manhattan Project was a top-secret research project that successfully created an atomic bomb during World War II. Its significance for wartime diplomacy was that it gave the United States a significant strategic advantage.
Step-by-step explanation:
The Manhattan Project was a top-secret research project launched during World War II with the goal of creating a deliverable atomic bomb. It employed over 100,000 people and successfully detonated an atomic explosion in July 1945. The significance of the Manhattan Project for wartime diplomacy was that it gave the United States a significant strategic advantage over its enemies and fundamentally changed the balance of power in international relations.