President Roosevelt, Winston Churchill and Stalin met from November 28 to December 1 in Tehran, Iran, to coordinate a second front. One of the most important achievements of the meeting was the agreement on global plans, especially those to launch Soviet attacks against Germany from the East at the same time as the Allied attack of the West. Finally, if Japan goes to war, the military strategy in the Far East will be defensive.  Although the ABC-1 agreement was not a military alliance, it meant that the United States was preparing to go to war on the allied side, that the United States would do everything to maintain the security of the British Commonwealth, and that the U.S. military was modifying existing war plans (for example. B RAINBOW plans) to integrate military integration and cooperation with other nations. The 1941 report of the 1941 U.S. General Staff Conference established general principles, resources and military intervention strategies for a common Allied military strategy. The British approach to the Nazi problem was sufficient for the original American plan. The British first called for a sun-tsu approach to attack the flanks and peripheries of Nazi interests (North Africa, the Middle East, etc.). On the other hand, the United States sought an approach based on Jomini a hammer, a mass battle with Nazi Germany.
The plan assumed that if the United States went to war against Nazi Germany, there would probably also be Fascist Italy and imperial Japan. The general principles of the agreement stipulated that prior to the bombing of Pearl Harbor, the United States had approved the ABC-1 agreement with the British. She said that if the United States entered the war, it would first focus its efforts on Germany. After the defeat of Germany, the Allies focused on Japan. In January 1943, President Roosevelt met Winston Churchill in Casablanca. Both agreed to strengthen the war in the Pacific, invade Sicily, increase pressure on Italy and insist on an “unconditional surrender” of the enemy. On May 7, 1945, the German government surrendered unconditionally. On 8 May the V-E (victory in Europe) was proclaimed. On April 12, 1945, President Roosevelt died suddenly of a brain haemorrhage. Harry S Truman took over as president. America has not been as affected by war as the rest of the world.
The war greatly helped the American economy and by the end of the war, GNP and citizens` disposable incomes had increased considerably. The Great Depression ended with the onslaught of military orders. Under the War Production Council (WPB), which oversaw war production in the United States, American factories produced an enormous amount of weapons, such as weapons and aircraft.