The Tehran conference lasted from November 28 to December 1, 1943. The heads of government of the USSR, the USA and Great Britain took part in it. The main issues of the conference were the military, in particular - the second front in Europe. Indeed, contrary to the obligations of the Anglo-American allies, it was never discovered by them either in 1942 or in 1943.
By that time, the Red Army had already achieved outstanding victories in the fight against fascism. Britain and America began to fear somewhat that if this continued, Soviet troops would be able to liberate Western Europe without their help. Therefore, it was decided to open a second front. Churchill and Roosevelt had different points of view on where, when and on what scale this operation should begin. The final point was made by the Soviet delegation. The Overlord Plan was approved. According to which, the second front was to be opened in May 1944, striking the enemy from the north-west and south of France. The Soviet Union, in turn, announced its intention to launch an offensive from its side at the same time, in order to prevent the possibility of transferring enemy forces from the Eastern to the Western Front.
It was decided to take the necessary measures in order to involve Turkey in the war against Germany, as well as to provide assistance to the partisans in Yugoslavia.
Considering that Japan repeatedly provided assistance to the Hitlerite army, despite the agreement on neutrality signed with Russia in 1941, the Soviet Union went to meet the United States and Great Britain and agreed to enter the war against Japan after the final victory over Germany.
Among other things, the conference discussed the post-war world order and the security of peoples. America and England proposed various options for the post-war structure of Germany, but not one of them was approved by Stalin. Therefore, it was suggested that this issue be referred to the European Consultative Commission. But it was decided to transfer the German Konigsberg (later renamed Kaliningrad) to the Soviet Union.
The Polish question was also considered. Roosevelt and Churchill wanted to persuade the Soviet delegation to renew relations with the Polish émigré government, which was at that time in London. The West planned to return him to Poland again in order to preserve the bourgeois system there. But Stalin did not go for it. But a preliminary agreement was reached that the post-war borders of Poland should pass along the "Curzon Line".
The Tehran Conference adopted the "Declaration on Iran", which guaranteed its independence and territorial inviolability.
As a result of the conference, on December 1, 1943, the Declaration of the Three Powers was adopted, which contributed to the rallying of the anti-Hitler coalition and testified to the readiness of states with different social systems to cooperate with each other in order to solve international problems.