The United States and the Soviet Union were never the coziest of allies during the Second World War, and when the Axis Powers were defeated, it became clear that they had drastically different visions for the future of the world, and that each saw themselves as leading the postwar order. The Cold War really began in Europe, over the fate of Eastern European nations, especially Poland. Franklin Roosevelt and Josef Stalin had agreed in principle at the Yalta Conference that Poland would have free and democratic elections. By the time the Potsdam Conference came around in 1945, however, it became clear that Stalin had different plans, and that Poland, and probably the rest of Eastern Europe would have a government friendly to the USSR. Talks at Potsdam soured when Harry Truman, emboldened by the recent success of the atomic bomb tests at Los Alamos, took a hard line with the Soviets. With the end of the war, the Americans increasingly took the view that Stalin had designs on conquering Europe, and the Soviets feared the influence of the United States in Europe, particularly in the western half of Germany. By the time the US announced billions of dollars in aid as part of the Marshall Plan in 1948, the two sides viewed each other as rivals, even enemies, operating within different, highly contested, spheres of influence.