Major Ally Powers

• United Kingdom, September 3, 1939
• Soviet Union, June 22, 1941
• United States of America, December 8, 1941

Minor Ally Powers

• Poland, September 1, 1939
• France, September 3, 1939
• Australia, September 3, 1939
• New Zealand, September 3, 1939
• Nepal, September 4, 1939
• Newfoundland, September 4, 1939
• Tonga, September 4, 1939
• South Africa, September 6, 1939
• Canada, September 10, 1939
• Denmark, April 9, 1940
• Norway, April 9, 1940
• Belgium, May 10, 1940
• Luxembourg, May 10, 1940
• Netherlands, May 10, 1940
• Free France, June 18, 1940
• Greece, October 28, 1940
• Kingdom of Yugoslavia, April 6, 1941
• Tannu Tuva, June 15, 1941
• Panama, December 7, 1941
• Philippines, December 7, 1941
• Costa Rica, December 8, 1941
• Dominican Republic, December 8, 1941
• El Salvador, December 8, 1941
• Haiti, December 8, 1941
• Honduras, December 8, 1941
• Nicaragua, December 8, 1941
• Republic of China, December 9, 1941
• Guatemala, December 9, 1941
• Cuba, December 9, 1941
• Provisional Government of the Republic of Korea, December 9, 1941 (Govt. in exile)
• Czechoslovakia, December 16, 1941 (Govt. in exile)
• Mexico, May 22, 1941
• Brazil, August 22, 1942
• Ethiopia, December 14, 1942
• Iraq, January 17, 1943
• Bolivia, April 7, 1943
• Iran, September 9, 1943
• Italy, October 13, 1943 (formerly a member of the Axis)
• Colombia, November 26, 1943
• Liberia, January 27, 1944
• Romania, August 25, 1944 (formerly a member of the Axis)
• Bulgaria, September 8, 1944 (formerly a member of the Axis)
• Finland, September 19, 1944 (formerly a member of the Axis)
• San Marino, September 21, 1944
• Albania, October 26, 1944 (formerly a member of the Axis)
• Hungary, January 20, 1945 (formerly a member of the Axis)
• Bahawalpur, February 2, 1945
• Ecuador, February 2, 1945
• Paraguay, February 7, 1945
• Peru, February 12, 1945
• Uruguay, February 15, 1945
• Venezuela, February 15, 1945
• Turkey, February 23, 1945
• Lebanon, February 27, 1945
• Saudi Arabia, March 1945
• Argentina, March 27, 1945
• Chile, April 11, 1945
• People's Republic of Mongolia, August 9, 1945

Major Axis Powers

• Nazi Germany, Invaded Poland, September 1, 1939.
• Fascist Italy, Invaded Albania, 1939
• Imperial Japan, Attacks Pearl Harbor, December 7, 1941

Minor Axis Powers

• Hungary, November 20, 1940
• Romania, November 23, 1940
• Bulgaria, March 1, 1941
• Yugoslavia, March 25, 1941

Co-Belligerents

• Finland, June 25, 1941
• Thailand, December 21, 1941

Japanese Puppet States

• Manchukuo (Manchuria), Japanese puppet from the outset
• Mengjiang (Inner Mongolia), Japanese puppet from the outset
• China (Reorganised Government of China at Nanking), March 29, 1940
• Burma, August 1, 1942
• India (Provisional Government of Free India), October 21, 1943

Italian Puppet State

• Albania, April 12, 1939

German Puppet States

• Slovakia, March 23, 1939
• Croatia, April 10, 1941
• Norway (Quisling regime, February, 1942)
• Italian Social Republic, September 23, 1943

Axis Collaborator States

• Denmark (Protectorate Government, April, 1940)
• France (Vichy regime), June 22, 1940

Axis Sympathizer States

• Spain
• Argentina