After the German attack on the USSR and the failure of the Blitzkrieg on the Eastern Front, the international situation changed dramatically. W. Churchill’s radio address on June 22, a statement at a press conference on June 24, 1941 by F. Roosevelt on USSR support and assistance were declarative in nature, as was the Soviet-British agreement on joint actions in the war against Germany concluded on July 12, 1941. The defeat of the Soviet Union was seen in the West after the “Finnish experience of the USSR” as inevitable, and diplomatic efforts were pursued only by gaining time for their own needs, including the creation of an anti-Hitler coalition consisting of, first of all, Britain and the United States. On August 14, 1941, these countries signed a corresponding document, the Atlantic Charter, calling for the formation of an anti-Hitler coalition.

However, the prospect of a protracted war of Germany on the Eastern Front made it necessary to re-evaluate the USSR as a military power and as a potential ally country. This was also facilitated by numerous diplomatic and military missions, among which the visit to the USSR by advisor to the President of the United States G. Hopkins in July-August 1941 should be highlighted. On August 25, 1941, after the joint introduction of British and Soviet troops into pro-German Iran (in accordance with 6 of the Soviet-Iranian Treaty of 1921), there was another prerequisite for rapprochement, providing sous-hop connection of potential allies.

The outcome of this process was the accession of the USSR on September 24, 1941 to the "Atlantic Charter" at the I Allied Conference and the start of negotiations on the supply of weapons and military equipment to the Soviet Union at the Soviet-Anglo-American Conference in Moscow from September 29 to October 1, 1941. in the September days of 1941, the first declarative period of the formation of the anti-fascist coalition ended.

The main content of the new stage, which lasted until the Moscow Conference of 1943, was the formation of economic cooperation between the USSR and the coalition countries. Of particular importance was the supply of Lend-Lease, which took place mainly through the Allied-occupied Iran (23.8%), across the Pacific Ocean (47.1%) and to a lesser extent the Northern Sea Route (22.7%). Already in September 1941, preparations were being made to increase the capacity of the Iranian railway by 6 times. Since 1942, this route, like the North, began to operate effectively (with some interruption in July-August 1942). If in 1941, Lend-Lease deliveries were symbolic, then since 1942 they have resulted in substantial USSR assistance of $ 11.2 billion ($ 9.8 billion - the US share). In the USSR, 427 thousand trucks, 13.5 thousand tanks, more than 22 thousand aircraft, 4.5 million tons of food, etc. were delivered.

Although these figures were inferior to the total USSR production during the war years by more than 20 time, their strategic character is undoubted: every ninth tank, every seventh aircraft that fought in the Red Army, was foreign-made. Lend-Lease deliveries were accompanied by fairly large losses caused by the opposition of Germany. Of the 2,660 vessels with a cargo of 16.5–17.5 million tons, about 100 ships with 1.5 million tons of cargo did not reach the points of destination. The main losses fell on the Northern route, where 85 of 1520 transports were sunk. The most famous was the tragedy of the caravan of ships PQ-17, which lost 24 ships, while only 11 reached the Soviet ports.

During this period, the legalization of the anti-Hitler coalition also ended. The events of December 7, 1941 at the US naval base in Pear l Harbor (Hawaii), where the Japanese had almost completely perfidiously destroyed the US Pacific fleet, led to the declaration of war against Japan on December 8, 1941 by the United States and England. On December 11, 1941, the United States declared war on Germany and Italy. All the great states were embroiled in a world war.

The strengthening of the anti-Hitler coalition was also supported by the United Nations Declaration, signed on January 1, 1942 in Washington by representatives of 4 great powers (USSR, USA, England and China) and 22 other states, as well as the Soviet-English treaty on May 26, 1942. and the Soviet-American agreement of June 11, 1942. By the beginning of military operations with Japan in 1945, the coalition included 56 states.

Due to the position of England and William Churchill, military-strategic cooperation had a second-degree character, and military operations of the USSR and allies were little connected until 1943. Political and military-strategic decisions were made mainly by F. Roosevelt and W. Churchill at their numerous personal meetings, who took more than 120 days during the war. Stalin was only informed about them, and all the requests of the USSR to open a second front in Europe were practically ignored.

The opening of the second front was envisaged only in the event of a close defeat of the USSR or Germany to prevent Soviet penetration into "civilized" Europe. At the same time, it should be noted that, although the Eastern Front was the main one, a number of Allied operations during the specified period were of a strategic nature (naval battles in the Coral Sea from May 7–8, 1942, near Midway on June 4–6, 1942 ., Operation Torch - the landing of Allied forces in North Africa with a simultaneous attack from Egypt from 2-8 November 1942, etc.). Allied victories in 1942. weakened the countries of the fascist camp, primarily Japan and to a lesser extent Germany.