Cold War antagonism between the Soviet Union and the United States began in the final moments of World War II. For a week in February 1945, the "Big Three"-the leaders of Great Britain, the Soviet Union, and the United States-met in the Crimean city of Yalta to discuss final war aims and the postwar world. The Allies appeared to be in harmony, but cracks were already forming in what President Franklin Roosevelt called the "Grand Alliance." Agreement was reached on two of his chief concerns-the formation of the United Nations and support of Soviet troops for the war against Japan. But left unresolved was the nature of a postwar Germany and the extent of Soviet influence in Eastern Europe. These issues, colored by the three countries' radically different ideas of national security, were the roots of Cold War hostility.