Countries Involved in World War Two (WWII)

While a surprising number of countries are currently at war, all of today's conflicts combined would still be far smaller than World War II. Involving more than 100 million people from dozens of nations (many more than in World War I) spread all across the globe, WWII was the biggest war in human history. It was also the deadliest war in history, resulting in an estimated 21-25 million military casualties and 50-55 civilian deaths—including the more than 6 million Jews who were killed in Nazi concentration camps. Leading up to the war, many countries attempted to remain neutral. However, as the conflict raged on, more and more countries were forced to join one of two sides: the Allies and the Axis Powers.

Both of these alliances changed and morphed over the course of the war, with countries coming and going as battles were won and lost, territories were taken and liberated, and political agreements were forged and dissolved. Several countries started out as neutral but were eventually drawn into the conflict, or initially fought for one side, but switched to the other (often after a forceful change in government). As a result, several countries were both Allies and Axis, or both neutral and either Allies/Axis.

Which countries joined the Allies in World War II?

When World War II began in 1939, the Allies were France, Poland, and the United Kingdom. Days later, the independent British dominions of Australia, Canada, New Zealand, and South Africa joined. As the war continued, more and more countries joined the Allies—including two major powers which had intended to remain neutral.

The first of these powers was Russia, which had signed a non-aggression pact with Germany and had even participated in Germany's initial invasion of Poland. However, when Germany broke that pact and invaded Russia in Operation Barbarossa in June 1941, Russia quickly joined the Allies.

The second formerly neutral power was the United States, whose entry into the war was prompted by Axis power Japan's attack on Pearl Harbor in December 1941. China also joined the Allies in December 1941—though the country had already been at war with Japan since 1937.

The Allied countries were led by the "Four Powers," which consisted of the "Big Three"—the United Kingdom, United States, and Russia—as well as China. More than twenty additional countries also contributed to the cause. The Allies would formalize their union with the Declaration of United Nations, which was signed by the Four Powers on January 01, 1942, and 22 more countries on January 02. The declaration would become the United Nations Charter with the formal launch of the United Nations in 1945.

Countries on the Allies side in WWII:

Country Date Joined Country Date Joined Country Date Joined
Argentina 27 March 1945 Finland* 15 Sept. 1944 Oman 10 Sept. 1939
Australia 3 Sept. 1939 France 3 Sept. 1939 Panama 7 Dec. 1941
Belgium 10 May 1940 Greece 28 Oct 1940 Paraguay 7 Feb. 1945
Bolivia 7 Apr. 1943 Guatemala 9 Dec. 1941 Peru 12 Feb. 1945
Brazil 22 Aug. 1942 Haiti 8 Dec 1941 Philippines 8 Dec 1941
British India 3 Sept. 1939 Honduras 8 Dec. 1941 Poland 1 Sept. 1939
Bulgaria* 8 Sept. 1944 Iran 9 Sept. 1943 Romania* 25 Aug. 1944
Canada 10 Sept. 1939 Iraq 16 Jan. 1943 Saudi Arabia 1 Mar. 1945
Chile 11 April 1945 Lebanon 27 Feb. 1945 South Africa 6 Sept. 1939
China 9 Dec 1941 Italy* 10 Oct. 1943 South Korea* 10 Dec. 1941
Colombia 26 July 1943 Liberia 27 Jan. 1944 Soviet Union 22 June 1941
Costa Rica 8 Dec. 1941 Luxembourg 10 May 1940 Syria 26 Feb. 1945
Cuba 9 Dec. 1941 Mexico 22 May 1942 Turkey 23 Feb. 1945
Czechoslovakia* 16 Dec. 1941 Mongolia 1 Aug 1945 United Kingdom 3 Sept. 1939
Denmark 8 Apr. 1940 Nepal 4 Sept. 1939 United States 8 Dec. 1941
Dominican Rep. 8 Dec. 1941 Netherlands 10 May 1940 Uruguay 15 Feb. 1945
Ecuador 2 Feb. 1945 New Zealand 3 Sept. 1939 Venezuela 15 Feb. 1945
Egypt 24 Feb. 1945 Nicaragua 8 Dec. 1941 Vietnam (Viet Minh) 7 Dec. 1941
El Salvador 8 Dec. 1941 Norway 8 Apr. 1940 Yugoslavia 6 Apr. 1941
Ethiopia 14 Dec. 1942

* Notes:

  • Bulgaria was a former Axis nation.
  • Czechoslovakia's government was in exile at the time of declaration.
  • Finland fought alongside Germany and against Russia in the Continuation War from 1941-1944, declared war on Germany on 3 March 1945, but made the declaration retroactive to 15 September 1944.
  • Italy and Romania were former Axis nations.
  • South Korea's government was provisional.
  • Vietnam's allegiance came courtesy of the Viet Minh.

Which countries joined the Axis powers in World War II?

The three major Axis powers were Germany, Italy, and Japan, which banded together under a series of agreements, culminating in the Tripartite Pact of 1940. Six additional nations then joined the Tripartite Pact. The first four were fairly straightforward: Hungary on November 20, 1940, Romania on November 23, Slovakia on November 24, Bulgaria on March 1, 1941.

The final two signatories on the Tripartite Pact come with caveats. First is Yugoslavia, whose government feared a German invasion if they chose to resist, and so signed the pact on March 25, 1941—however, the government was promptly overthrown by a coup and the new government rejected the agreement a mere two days later. (This act prompted Germany to add Yugoslavia to the list of countries it had invaded.) Lastly, the German-Italian puppet state of Croatia signed on April 10, 1941, despite the fact that it was an illegitimate nation with no actual authority to do so.

In addition to the Tripartite Pact, certain other countries signed what was known as the Anti-Comintern Pact, which was much less demanding. Many Anti-Comintern countries were allowed to remain neutral or required to send only volunteer troops to join the Nazi army. Even less binding were the Bilateral Pacts that other countries (as well as a few illegitimate governments and Nazi-installed puppet states) agreed to follow. Additionally, the Axis powers, particularly Japan, also made extensive use of "puppet states," in which a newly overtaken country's existing government would be replaced by a new (typically illegitimate) government that operated on its own but took its orders from the "puppetmaster" country.

Countries on the Axis side in WWII:

Country Nature Country Nature
Bulgaria Axis Laos* puppet state
Burma (Ba Maw govt)* bilateral pact Manchuko* puppet state
Cambodia (Kampuchea)* puppet state Mongolia (Mengjiang)* puppet state
Croatia Axis Philippines (Second Republic)* puppet state
Denmark* Anti-Comintern Romania Axis
Finland* Anti-Comintern Slovakia Axis
Germany Axis Soviet Union* bilateral pact
Greece (Hellenic States) puppet state Spain Anti-Comintern
Hungary Axis Thailand bilateral pact
India (Azad Hind)* puppet state Vichy France* puppet state
Iraq bilateral pact Vietnam (Empire of Vietnam)* puppet state
Italy Axis Yugoslavia* non-ratified
Japan Axis

* Notes:

  • Denmark's contributions were minimal and it would likely have remained neutral if it had not been occupied by Germany during much of the war.

  • Finland never actually joined the Axis, but fought alongside Germany against Russia in the Continuation War from 1941-1944.

  • The Soviet Union helped Germany invade Poland before switching to the Allies.

  • Yugoslavia agreed to join the Axis, but the agreement was rejected two days later after a government coup.

  • All other Axis countries marked with * were puppet states, illegitimate governments, or both.

Which countries remained neutral in World War II?

As difficult a task as it was, several countries did manage to remain neutral during World War II. Many officially neutral countries nonetheless offered limited support to one side or the other, such as sending volunteer troops or allowing passage through their territory.

Neutral Countries in WWII:

Afghanistan Latvia Spain
Andorra Liechtenstein Sweden
Bhutan Lithuania Switzerland
Estonia Monaco Tibet
Iceland Portugal Turkey
Iran San Marino Vatican City
Ireland Saudi Arabia Yemen

When did WWII start and end?

It is generally accepted that World War II began on September 1, 1939, when German troops invaded Poland, prompting the leaders of France and Britain to declare war two days later. However, as this conflict expanded, it merged with existing hostilities between Japan and several other countries in Asia. Because of this, some historians suggest that WWII actually began as early as July 7, 1937, the start of the Second Sino-Japanese War, or when Japan invaded Manchuria on September 19, 1931. The war's end date is also debatable. Most historians agree that the end date was August 14, 1945, also known as V-J (Victory over Japan) day. Technically, however, the war didn't end until September 2, 1945, the day Japan formally surrendered.

Countries Involved in World War Two (WWII)

Note: Many countries have complex histories during WWII. See notes for clarification. Also, list includes notable occupied territories and puppet insurgencies that were not officially recognized countries and were dissolved at the war's conclusion.

Countries Involved in World War Two (WWII)