The Second World War was the second armed conflict in a world level, considered as one of the most intense in the history of mankind. Positioned in opposite sides the Allies, winners, and the Axis, defeated.
It's calculated the number of participant countries had been 61.
The following tables show the many participant countries in the Second World War within the two existent coalitions, with the beginning of its participation in this conflict. Besides that, are also showed the countries that had opted to remain neutral towards the events.
| Country | Date |
| Allies | |
| Poland | September 1, 1939 |
| New Zealand | September 3, 1939 |
| United Kingdom | September 3, 1939 |
| France | September 3, 1939 |
| Australia | September 3, 1939 |
| South Africa | September 6, 1939 |
| Canada | September 10, 1939 |
| Denmark | April 9, 1940 |
| Norway | April 9, 1940 |
| Luxembourg | May 10, 1940 |
| Belgium | May 10, 1940 |
| Holland | May 10, 1940 |
| Greece | October 28, 1940 |
| Yugoslavia | April 6, 1941 |
| Soviet Union | June 22, 1941 |
| Iran | August 25, 1941 |
| India | December 7, 1941 |
| Panama | December 7, 1941 |
| United States of America | December 7, 1941 |
| China | December 8, 1941 |
| Costa Rica | December 8, 1941 |
| Dominican Republic | December 8, 1941 |
| El Salvador | December 8. 1941 |
| Haiti | December 8, 1941 |
| Honduras | December 8, 1941 |
| Cuba | December 9, 1941 |
| Guatemala | 9 December 1941 |
| Nicarágua | December 11, 1941 |
| Checkoslovakia | December 16, 1941 |
| Mexico | May 22, 1942 |
| Ethiopia | Julho 14, 1942 |
| Brazil | August 22, 1942 |
| Iraq | January 17, 1943 |
| Bolivia | April 7, 1943 |
| Colombia | November 26, 1943 |
| Liberia | January 27, 1944 |
| San Marino | September 21 1944 |
| Saudi Arabia | February 1, 1945 |
| Equador | February 2, 1945 |
| Paraguai | February 7, 1945 |
| Peru | February 12, 1945 |
| Uruguay | February 15, 1945 |
| Venezuela | February 15, 1945 |
| Turkey | February 23, 1945 |
| Egypt | February 24, 1945 |
| Lebanon | February 27, 1945 |
| Argentina | February 27, 1945 |
| Chile | April 11, 1945 |
| Axis | |
| Germany | September 1, 1939 |
| Soviet Union | September 17, 1939 |
| Italy | June 10, 1940 |
| Hungary | June 20, 1940 |
| Romania | November 23, 1940 |
| Bulgaria | March 1, 1941 |
| Finland | June 25, 1941 |
| Japan | December 7, 1941 |
| Neutrals | |
| Portugal | - |
| Spain | - |
| Sweden | - |
| Turquia until 1945 | - |
| Switzerland | - |
| Ireland Republic (former-EIRE) | - |
| Iceland | - |
