- Western Front: France, Belgium, the Netherlands, Luxembourg, Germany, and Italy.
- Eastern Front: Poland, the Baltic States (Estonia, Latvia, Lithuania), Finland, the Soviet Union (including Ukraine, Belarus, and Western Russia), Romania, Hungary, and Czechoslovakia.
- Mediterranean Front: Italy, Greece, Yugoslavia, Albania, North Africa (including Egypt, Libya, Tunisia, Algeria, and Morocco), Malta, Sicily, and Crete.
- Atlantic Ocean: U-boat campaigns and the Battle of the Atlantic.
Asia:
- China-Burma-India Theater: China, Burma (Myanmar), India, and Nepal.
- Pacific Theater: Japan, China, the Philippines, Indonesia (Dutch East Indies), Malaysia, Singapore, Thailand, Burma, New Guinea, the Solomon Islands, the Bismarck Archipelago, the Gilbert Islands, the Marshall Islands, the Caroline Islands, the Mariana Islands, and Okinawa (Ryukyu Islands).
Africa:
- North African Campaign: Egypt, Libya, Tunisia, Algeria, and Morocco.
- East African Campaign: Kenya, Ethiopia, Eritrea, Somalia, and Sudan.
- Madagascar: Invasion and occupation of Madagascar.
Middle East:
- Iraq: Anglo-Iraqi War and British occupation.
- Syria and Lebanon: Allied invasion and establishment of the Free French mandate.
South America:
- Brazil: Declaration of war on Germany and Italy, sending a naval force to the Atlantic.
South Pacific:
- New Zealand: Naval base and supply depot for Allied operations in the Pacific.
North America:
- United States: Production and supply of war materials, training of troops, and deployment in various theaters of war.
- Canada: Production and supply of war materials, training of troops, and deployment in various theaters of war.