In late December 1941 Churchill and Roosevelt met at the Arcadia Conference, which established a joint strategy between the U.S. and Britain.

Both agreed on a Europe first strategy that prioritized the defeat of Germany before Japan.
The U.S. and Britain established the Combined Chiefs of Staff to coordinate military policy and the Combined Munitions Assignments Board to coordinate the allocation of supplies.
An agreement was also reached to establish a centralized command in the Pacific theater called ABDA, named for the American, British, Dutch, and Australian forces in the theater.
On January 1, 1942, the United States, Britain, China, the Soviet Union, and twenty-two other countries (the Allied Powers) issued the Declaration by United Nations, in which each nation pledged to defeat the Axis powers.

In 1942, Roosevelt formed a new body, the Joint Chiefs of Staff, which made the final decisions on American military strategy.
Admiral Ernest J. King as Chief of Naval Operations commanded the Navy and Marines, while General George C. Marshall led the Army and was in nominal control of the Air Force, which in practice was commanded by General Hap Arnold.
The Joint Chiefs were chaired by Admiral William D. Leahy, the most senior officer in the military.
Roosevelt avoided micromanaging the war and let his top military officers make most decisions.
Roosevelt's civilian appointees handled the draft and procurement of men and equipment, but no civilians – not even the secretaries of War or Navy – had a voice in strategy.
Roosevelt avoided the State Department and conducted high-level diplomacy through his aides, especially Harry Hopkins, whose influence was bolstered by his control of the Lend Lease funds.
In late December 1941 Churchill and Roosevelt met at the Arcadia Conference, which established a joint strategy between the U.S. and Britain.
Both agreed on a Europe first strategy that prioritized the defeat of Germany before Japan. The U.S. and Britain established the Combined Chiefs of Staff to coordinate military policy and the Combined Munitions Assignments Board to coordinate the allocation of supplies. An agreement was also reached to establish a centralized command in the Pacific theater called ABDA, named for the American, British, Dutch, and Australian forces in the theater. On January 1, 1942, the United States, Britain, China, the Soviet Union, and twenty-two other countries (the Allied Powers) issued the Declaration by United Nations, in which each nation pledged to defeat the Axis powers.
In 1942, Roosevelt formed a new body, the Joint Chiefs of Staff, which made the final decisions on American military strategy. Admiral Ernest J. King as Chief of Naval Operations commanded the Navy and Marines, while General George C. Marshall led the Army and was in nominal control of the Air Force, which in practice was commanded by General Hap Arnold. The Joint Chiefs were chaired by Admiral William D. Leahy, the most senior officer in the military. Roosevelt avoided micromanaging the war and let his top military officers make most decisions. Roosevelt's civilian appointees handled the draft and procurement of men and equipment, but no civilians – not even the secretaries of War or Navy – had a voice in strategy. Roosevelt avoided the State Department and conducted high-level diplomacy through his aides, especially Harry Hopkins, whose influence was bolstered by his control of the Lend Lease funds.
Franklin D. Roosevelt