While both World War I and World War II were global in scale and involved dozens of countries, both wars also saw those countries coalescing into two opposing groups. The countries involved in World War I aligned with either the Central Powers (Germany, Turkey, Austria-Hungary) or the Allies (France, Russia, Great Britain). Two decades later, the countries involved in World War II followed suit, again aligning themselves with either the German-led coalition—now called the Axis Powers—or the Allies. While many countries successfully avoided joining either side during World War I, the list of countries who remained neutral in World War II was much shorter, as the conflict expanded to engulf nearly the entire globe.
Allies and Associated Powers in World War I:
In World War I, the Allies were also known as the Entente Powers. The Allies were led throughout much of the war by Great Britain, France, and Russia, who formalized their alliance with the Treaty of London, which was signed on the 5th of September, 1914. Allied forces were further subdivided into two groups: the Allies and the "Associate Powers," which were countries fighting alongside the Allies, but which stopped short of officially joining the coalition for political purposes. Finally, the Allies included several countries who officially declared war on the Central Powers, but did not participate in the military conflict.
|Asir (now part of Saudi Arabia)||associated|
|Australia (as part of British Empire)||ally|
|Bangladesh (as part of British Empire)||ally|
|Canada (as part of British Empire)||ally|
|Costa Rica||associated, non-combative|
|Czechoslovakia* (now Czech Republic and Slovakia)||associated|
|Finland (as part of Russia)||ally|
|France (and colonies)||ally|
|Hejaz/Hedjaz (now part of Saudi Arabia)||associated|
|India (as part of British Empire)||ally|
|Italy (and colonies)||ally|
|Myanmar (as part of British Empire)||ally|
|Nejd and Hasa (now part of Saudi Arabia)||associated|
|Nepal (as part of British India)||ally|
|New Zealand (as part of British Empire)||ally|
|Newfoundland (as part of British Empire)||ally|
|Nigeria (as part of British Empire)||ally|
|Oman (as part of British Empire)||ally|
|Pakistan (as part of British Empire)||ally|
|Siam (now Thailand)||associated|
|South Africa (as part of British Empire)||ally|
|United Kingdom (England, Ireland, and colonies)||ally|
- The Hejaz was a territory that revolted against Turkish rule in 1916 and was folded into what is now Saudi Arabia in 1932.
- Bosnia and Herzegovina, Montenegro, Serbia, and Slovenia would be among the countries that merged to form the Kingdom of Serbs, Croats, and Slovenes in 1918, which changed its name to Yugoslavia in 1929.
- Poland did not exist as an independent state throughout much of World War I, as its territory was split between occupiers from Russia, Germany, and Austria-Hungary. It was nonetheless the site of much of the Eastern Front's combat, and its people fought and suffered greatly. Poland was returned to independence as part of the Treaty of Versailles.
- Czechoslovakia did not exist as an independent state until 1918, instead comprising a portion of both Austria and Hungary.
- Luxembourg was officially neutral and never officially declared war upon the Axis powers despite the fact that it was occupied by Germany from 1914 to 1918. However, the country unofficially aligned itself with the Allies late in the war.
- San Marino declared its neutrality, but was forced into military participation by Italy.