Countries Involved in World War Two (WWII) 2025

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.