| Poland Declared War on Germany at | Midnight 31st August - 1st Sept 1939. [See the German White Book] | |
| Great Britain on Germany | September 3, 1939, 11 a.m. | |
| France on Germany | September 3, 1939, 5 p.m. | |
| India on Germany | September 3, 1939 | |
| Australia on Germany | September 3, 1939 | |
| New Zealand on Germany | September 3, 1939 | |
| Union of South Africa on Germany | September 6, 1939 | |
| Canada on Germany | September 10, 1939 | |
| Norway and Germany | No formal declaration of war | |
| Belgium and Germany | No formal declaration of war | |
| Luxembourg and Germany | No formal declaration of war | |
| The Netherlands on Germany | May 10, 1940 | |
| Italy on France | June 10, 1940 | |
| Canada on Italy | June 10, 1940 | |
| New Zealand on Italy | June 11, 1940 | |
| Australia on Italy | June 11, 1940 | |
| Union of South Africa on Italy | June 11, 1940 | |
| Greece on Italy | October 28,1940 | |
| Germany and Greece | No formal declaration of war | |
| Germany on Yugoslavia | April 6, 1941 | |
| Italy and Yugoslavia | No formal declaration of war | |
| Yugoslavia on Bulgaria | April 6, 1941 | |
| Yugoslavia on Hungary | April 10, 1941 | |
| Bulgaria on Greece | April 24, 1941 | |
| Bulgaria on Yugoslavia | April 24, 1941 | |
| Germany on USSR | June 22, 1941 | |
| Italy on USSR | June 22, 1941 | |
| Rumania on USSR | No formal declaration of war | |
| Finland on USSR | No formal declaration of war | |
| Hungary on USSR | June 27, 1941 | |
| Great Britain on Rumania | December 7, 1941 | |
| Great Britain on Hungary | December 7, 1941 | |
| Canada on Finland | December 7, 1941 | |
| Canada on Rumania | December 7, 1941 | |
| Canada on Hungary | December 7, 1941 | |
| Australia on Finland | December 8, 1941 | |
| Australia on Rumania | December 8, 1941 | |
| Australia on Hungary | December 8, 1941 | |
| Union of South Africa on Finland | December 8, 1941 | |
| Union of South Africa on Rumania | December 8, 1941 | |
| Union of South Africa on Hungary | December 8, 1941 | |
| New Zealand on Finland | December 7, 1941 | |
| New Zealand on Hungary | December 7, 1941 | |
| New Zealand on Rumania | December 7, 1941 | |
| Japan on the United States | December 7, 1941 | |
| Japan on the British Empire | December 7, 1941 | |
| Great Britain on Japan | December 8, 1941 | |
| The United States on Japan | December 8, 1941 | |
| Canada on Japan | December 8, 1941, as of December 7, 1941 | |
| Costa Rica on Japan | December 8, 1941 | |
| Dominican Republic on Japan | December 8, 1941 | |
| Guatemala on Japan | December 8, 1941 | |
| Haiti on Japan | December 8, 1941 | |
| Honduras on Japan | December 8, 1941 | |
| El Salvador on Japan | December 8, 1941 | |
| Panama on Japan | December 8, 1941 | |
| Cuba on Japan | December 9, 1941 | |
| The Netherlands on Japan | December 8, 1941 | |
| The Netherlands Indies on Japan | December 8, 1941 | |
| China on Japan | December 9, 1941 | |
| China on Germany | December 9, 1941 | |
| China on Italy | December 9, 1941 | |
| Union of South Africa on Japan | December 8, 1941 | |
| Australia on Japan | December 8, 1941 | |
| Free France on Japan | December 8, 1941 | |
| Germany on the United States | December 11, 1941 | |
| Italy on the United States | December 11, 1941 | |
| The United States on Germany | December 11, 1941 | |
| The United States on Italy | December 11, 1941 | |
| Costa Rica on Germany and Italy | December 11, 1941 | |
| Guatemala on Germany and Italy | December 11, 1941 | |
| Cuba on Germany and Italy | December 11, 1941 | |
| Nicaragua on Germany, Italy and Japan | December 11, 1941 | |
| Poland on Japan | December 11, 1941 | |
| Dominican Republic on Germany and Italy | December 11, 1941 | |
| Haiti on Germany and Italy | December 12, 1941 | |
| Honduras on Germany and Italy | December 12, 1941 | |
| El Salvador on Germany and Italy | December 12, 1941 | |
| Panama on Germany and Italy | December 12, 1941 | |
| Rumania on the United States | December 12, 1941 | |
| Bulgaria on the United States | December 13, 1941 | |
| Bulgaria on Great Britain | December 13, 1941 | |
| Hungary on the United States | December 13, 1941 | |
| Czechoslovakia on all countries that are in a state of war with Great Britain, theUnited States, or the USSR |
December 16, 1941 | |
| Albania on the United States | December 17, 1941 | |
| Nicaragua on Bulgaria, Hungary, & Rumania | December 20, 1941 | |
| Belgium on Japan | December 20, 1941 | |
| Haiti on Bulgaria, Hungary, and Rumania | December 24, 1941 | |
| Great Britain on Bulgaria | December 27, 1941, as of December 13, 1941 | |
| The Netherlands on Italy | December 30, 1941, as of December 11, 1941 | |
| Union of South Africa on Bulgaria | December 31, 1941, as of December 13, 1941 | |