The "Big Three" (Roosevelt, Churchill, and Joseph Stalin), together with Generalissimo Chiang Kai-shek, cooperated informally on a plan in which American and British troops concentrated in the West. About the book: https://www.amazon.com/gp/product/0375761268/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0375761268&linkCode=as2&tag=tra0c7-20&linkId=917f0e214bf0f1f947ababab8628550d
Soviet troops fought on the Eastern front, and Chinese, British and American troops fought in Asia and the Pacific. The Allies formulated strategy in a series of high-profile conferences as well as contact through diplomatic and military channels. Roosevelt guaranteed that the U.S. would be the "Arsenal of Democracy" by shipping $50 billion of Lend Lease supplies, primarily to Britain and to the USSR, China and other Allies.
In October 1942, the President was advised that military resources were desperately needed at Guadalcanal to prevent overrunning by the Japanese. FDR heeded the advice, redirected armaments and the Japanese Pacific offensive was stalled.
The Allies undertook the invasions of French Morocco and Algeria (Operation Torch) in November 1942. FDR very much desired the assault be initiated before election day, but did not order it. FDR and Churchill had another war conference in Casablanca in January 1943; Stalin declined an invitation. The Allies agreed strategically that the Mediterranean focus be continued, with the cross-channel invasion coming later, followed by concentration of efforts in the Pacific. Roosevelt also championed General Henri Giraud as leader of Free France against General Charles de Gaulle. Hitler reinforced his military in North Africa, with the result that the Allied efforts there suffered a temporary setback; Allied attempts to counterbalance this were successful, but resulted in war supplies to the USSR being delayed, as well as the second war front. Later, their assault pursued into Sicily (Operation Husky) followed in July 1943, and of Italy (Operation Avalanche) in September 1943. In 1943 it was apparent to FDR that Stalin, while bearing the brunt of Germany's offensive, had not had sufficient opportunity to participate in war conferences. The President made a concerted effort to arrange a one-on-one meeting with Stalin, in Fairbanks. However, when Stalin learned that Roosevelt and Churchill had postponed the cross-channel invasion a second time, he cancelled. The strategic bombing campaign was escalated in 1944, pulverizing all major German cities and cutting off oil supplies. It was a 50–50 British-American operation. Roosevelt picked Dwight D. Eisenhower, and not George Marshall, to head the Allied cross-channel invasion, Operation Overlord that began on D-Day, June 6, 1944. Some of the most costly battles of the war ensued after the invasion, and the Allies were blocked on the German border in the "Battle of the Bulge" in December 1944. When Roosevelt died on April 12, 1945, Allied forces were closing in on Berlin.
Meanwhile, in the Pacific, the Japanese advance reached its maximum extent by June 1942, when the U.S. Navy scored a decisive victory at the Battle of Midway. American and Australian forces then began a slow and costly progress called island hopping or leapfrogging through the Pacific Islands, with the objective of gaining bases from which strategic airpower could be brought to bear on Japan and from which Japan could ultimately be invaded. In contrast to Hitler, Roosevelt took no direct part in the tactical naval operations, though he approved strategic decisions. FDR gave way in part to insistent demands from the public and Congress that more effort be devoted against Japan; he always insisted on Germany first.