Answer :
The Yalta Conference in February 1945, attended by Roosevelt, Churchill, and Stalin, was the event that signified the rise of Stalin's influence and the decline of Roosevelt's health and political clout, setting the stage for the Cold War hence, answer is 1) Yalta Conference.
The conference that marked the increasing ascendance of Soviet leader Joseph Stalin and the perceived decline of President Franklin Delano Roosevelt was the Yalta Conference. This pivotal February 1945 meeting held in the Soviet Union saw the leaders of the United States, the United Kingdom, and the Soviet Union—Roosevelt, Churchill, and Stalin, respectively—negotiating postwar plans for Europe, discussing the creation of the United Nations, and confronting the question of Germany's reconstruction. While the deterioration of Roosevelt's health became apparent, Stalin's influence rose as he asserted the Soviet Union's interests in Eastern Europe, particularly through his maneuvers concerning Poland and Eastern Europe's future. The Yalta Conference laid the groundwork for the postwar division of Europe and heightened tensions that would blossom into the Cold War hence, answer is 1) Yalta Conference..