The leaders, known as the Big Three, chose the Iranian capital as the site for their parley, largely at Stalin’s behest. When first lady Eleanor Roosevelt and Roosevelt's daughter Anna voiced a desire to accompany the president, he said no women would be present. Subsequently, they were incensed to learn that Churchill’s wife, Clementine, and Madame Chiang Kai-shek of China had made the trip.
FDR biographer Doris Kearns Goodwin wrote that rather than feeling any trepidation about the dangers of a secret trip through war zones, Roosevelt was not only eager to meet again with his friend Churchill but also excited at the prospect of meeting Stalin for the first time.
Roosevelt promised Stalin that the Americans and the British would invade Nazi-occupied France, crossing the English Channel, in the spring of 1944. Until that point, Churchill favored a joint strike through the Mediterranean, pushing eastward through the Balkans. That strategy would have presumably secured British interests in the Middle East and India while curbing the Soviet advance into Eastern Europe. For his part, FDR, with the advent of an Allied victory, sought to break up the British Empire; his concessions to Stalin served that goal....
The leaders agreed that the Soviet Union would fight against Japan once the Nazis were beaten. They also promised to offer postwar economic assistance to Iran and guaranteed the host nation’s independence and territorial integrity.
Roosevelt outlined for Stalin his vision of the proposed world organization in which a future United Nations would be dominated by “four policemen” — the United States, Britain, China, and Soviet Union— who “would have the power to deal immediately with any threat to the peace and any sudden emergency which requires action.”
Their discussions about a postwar peace settlement were tentative at best. Nevertheless, they voiced their desire to cooperate after what they believed would be an inevitable German defeat. The meeting proved so friendly that Churchill, who mistrusted Stalin, later voiced concern about Roosevelt’s efforts to woo the Soviet leader."
"SOURCE: “AMERICA, BRITAIN, and RUSSIA: THEIR CO-OPERATION AND CONFLICT, 1941-1946” BY ROBERT MCNEIL (1953)"