This is a timeline of declarations of war during World War II.
A declaration of war is a formal act by which one nation goes to war against another. The declaration is usually the act of delivering a performative speech or the presentation of a signed document by an authorized party of a national government in order to create a state of war between two or more sovereign states. The official international protocol for declaring war was defined in The Hague Peace Conference of 1907 (or Hague II).[1] For the diplomatic maneuvering behind these events, which led to hostilities between nations during World War II, see Diplomatic history of World War II.
Below is a table showing the outbreak of wars between nations which occurred during World War II. Indicated are the dates (during the immediate build-up to, or during the course of, World War II), from which a de facto state of war existed between nations. The table shows both the "Initiator Nation(s)" and the nation at which the aggression was aimed, or "Targeted Nation(s)". Events listed include those in which there were simple diplomatic breaking of relations that did not involve any physical attack, as well as those involving overt declarations or acts of aggression. In rare cases, war between two nations occurred twice, with an intermittent period of peace. The list here does not include peace treaties or periods of any armistice.
Key to type (fourth column):
A = Attack without prior, formal declaration of war;
C = Declaration and/or attack without standard, formal procedure, sometimes preceded by a casus belli thus fait accompli;
U = State of war arrived at through use of ultimatum;
W = Formal declaration of war made.
Date | Initiator nation(s) | Targeted nation(s) | Type | Notes/comments | Document/event |
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1939-09-01 | ![]() |
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A | German attack began at 4:44 a.m., Berlin and Warsaw time.[2][3][4] | Invasion |
1939-09-01 | ![]() |
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A | Invasion | |
1939-09-03 | ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
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U[3][5] | At 11:15 a.m. London time,[6] British PM, Neville Chamberlain publicly delivered his Ultimatum Speech.[a][5][7] As the Statute of Westminster 1931 was not yet ratified by the parliaments of Australia and New Zealand, the British declaration of war on Germany also applied to those dominions. Tonga was not a British dominion, but declared war separately, alongside Britain.[8] The French ultimatum to Germany expired a few hours later at 17:00. | United Kingdom declaration French declaration |
1939-09-04 | ![]() |
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W |
Declaration | |
1939-09-06 | ![]() |
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W[3][5] | Declaration | |
1939-09-10 | ![]() ![]() ![]() |
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W[3][5] | Declaration
Declaration | |
1939-09-17 | ![]() |
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A[3][5] | Invasion | |
1939-11-09 | ![]() |
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W | Kuwaiti Declaration of War | |
1939-11-30 | ![]() |
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A[3][5] | Second war between these nations (after Finnish invasion in 1918–1920). | Invasion |
1940-04-09 | ![]() |
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A[3] | Invasion of Denmark Invasion of Norway | |
1940-04-12 | ![]() |
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A[5] | Invasion | |
1940-05-10 | ![]() |
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A/W[3][5] | Date of the German offensive in the West, W from Belgium and the Netherlands.[9] | |
1940-05-10 | ![]() |
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A[5] | Luxembourg | |
1940-05-10 | ![]() |
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A | Invasion | |
1940-06-10 | ![]() |
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W[3][5] | France and the UK | |
1940-06-10 | ![]() |
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W[3] | Declaration | |
1940-06-11 | ![]() ![]() ![]() |
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W[3] |
South Africa Australia New Zealand | |
1940-06-11 | ![]() |
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W[3] | Declaration | |
1940-07-03 | ![]() |
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A | Vichy France cuts off diplomatic relations with the United Kingdom on 8 July 1940. | Attack |
1940-09-09 | ![]() |
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A | Egypt never formally declared war on Italy. | Invasion |
1940-09-22 | ![]() |
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A | Japanese troops occupy French Indochina | Invasion |
1940-09-23 | ![]() ![]() ![]() |
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A | Invasion | |
1940-10-?? | ![]() |
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A | Franco-Thai War | |
1940-10-28 | ![]() |
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U[5] | Italy invades Greece | Invasion |
1940-11-23 | ![]() |
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W[10] | Declaration | |
1941-02-05 | ![]() |
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A | Invasion | |
1941-04-06 | ![]() |
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W[3][5] | Invasion | |
1941-04-06 | ![]() |
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A[3][5] | Invasion | |
1941-04-06 | ![]() |
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A[5] | Invasion | |
1941-04-07 | ![]() |
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A[11] | After the German invasion, bombing of Hungarian locations | Invasion |
1941-04-14 | ![]() |
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A | Egypt did not formally declare war until 1945. | Invasion |
1941-05-02 | ![]() |
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A | Invasion | |
1941-06-08 | ![]() |
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A | [citation needed] | Invasion |
1941-06-22 | ![]() ![]() ![]() |
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W[5] | A timed declaration of war was given by Germany at the time of the attack[12] | Invasion |
1941-06-22 | ![]() Tuva |
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W | Tuva was a client state of the Soviet Union. Part of the USSR from 1944. | |
1941-06-24 | ![]() |
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A[5] | Bulgaria declares war on Greece and Yugoslavia. | |
1941-06-25 | ![]() |
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W | Finland recognized a state of war with the Soviet Union; third war between these nations. | Continuation War |
1941-06-27 | ![]() |
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C[11] | After the bombing of several Hungarian locations, the Hungarian military concluded a Soviet attack, the Government had decided the two countries were already belligerent, without the consent of the Parliament, in absence of the Regent | Invasion |
1941-08-25 | ![]() ![]() ![]() |
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A | Invasion | |
1941-12-05 | ![]() |
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W[13] | Declaration | |
1941-12-06 | ![]() ![]() |
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W[5] | Declaration | |
1941-12-07 | ![]() |
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W[14] | UK declaration of war from 1941-12-05 entered into force on 1941-12-07 1 minute after midnight | Declaration |
1941-12-07 | ![]() |
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A | A formal message breaking off diplomatic talks was sent before but arrived after the attacks began, but this was not a declaration of war.[15] See Attack on Pearl Harbor § Japanese declaration of war |
Declaration published after: |
1941-12-07 | ![]() ![]() ![]() |
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W[5] | Declaration | |
1941-12-07 | ![]() ![]() ![]() |
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W[5] | Declaration | |
1941-12-08 | ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
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W[5] |
British declaration
| |
1941-12-08 | ![]() |
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W[5] | South African declaration | |
1941-12-08 | ![]() |
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W[citation needed] |
Mongolian declaration | |
1941-12-08 | ![]() |
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W[5] |
Manchukuo declaration | |
1941-12-08 | ![]() |
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A | Invasion of Malaya | |
1941-12-09 | ![]() ![]() ![]() |
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W[5] |
Australian declaration New Zealand's declaration | |
1941-12-09 | ![]() |
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W[5] | China and Japan had been at undeclared war since 1937 | Second Sino-Japanese war
Declaration |
1941-12-11 | ![]() ![]() |
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W[3][5] | ||
1941-12-11 | ![]() ![]() ![]() ![]() ![]() ![]() |
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W[5] | Germany | |
1941-12-11 | ![]() |
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W[5] | Declaration | |
1941-12-11 | ![]() |
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W[3] | Japan rejected declaration of War. Prime Minister Hideki Tōjō's answer was: "We don't accept the Polish declaration of war. The Poles, fighting for their freedom, declared war under the British pressure"[citation needed]. | |
1941-12-12 | ![]() ![]() ![]() |
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W[5] |
Romanian declaration Bulgarian declaration | |
1941-12-12 | ![]() ![]() ![]() |
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W[5] | Declaration | |
1941-12-12 | ![]() ![]() |
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A | Portugal maintained neutrality throughout World War II. | |
1941-12-13 | ![]() ![]() ![]() |
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W[5] |
British declaration New Zealand's declaration South African declaration | |
1941-12-13 | ![]() |
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W[5] | Declaration | |
1941-12-13 | ![]() |
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W[5] | Declaration | |
1941-12-14 | ![]() |
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W[5] | Declaration | |
1941-12-15 | ![]() |
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C[16] | The Prime Minister informed the U.S. ambassador without approval of the Parliament and the Regent, but initially denied it would mean "war" in fact, however two days later he declared it means the two countries became belligerent. As the ambassador refused to accept the verbal form of this act, the next day the Prime Minister in written reinforced it. | Declaration |
1941-12-16 | ![]() |
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W[5] | Czechoslovakia declares war on all countries at war with the United States of America, Great Britain and the Union of Soviet Socialist Republics. | Declaration |
1941-12-16 | ![]() |
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A | Invasion | |
1941-12-17 | ![]() |
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W | Declaration | |
1941-12-19 | ![]() |
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W[5] | Declaration | |
1941-12-19 | ![]() |
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W[17] | Out of the Axis countries only Romania reciprocated, declaring war on Nicaragua on the same day | Declaration |
1941-12-20 | ![]() |
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W | Declaration | |
1941-12-24 | ![]() |
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W[5] | Declaration | |
1941-12-24 | ![]() |
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W[18] | Out of the Axis countries only Romania reciprocated, declaring war on Haiti on the same day | Declaration |
1942-01-01 | United Nations | Axis Powers | W | Declared during Arcadia Conference | Declaration |
1942-01-06 | ![]() |
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W | Declaration | |
1942-01-25 | ![]() |
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A | Declaration | |
1942-01-25 | ![]() ![]() ![]() |
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W |
British declaration New Zealand's declaration South African declaration | |
1942-02-19 | ![]() |
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A | Portugal maintained neutrality throughout World War II. | Invasion |
1942-03-02 | ![]() |
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W[5] |
Australian declaration | |
1942-05-05 | ![]() ![]() ![]() |
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A | Invasion | |
1942-05-05 | ![]() ![]() ![]() ![]() ![]() ![]() |
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A | Invasion | |
1942-05-22 | ![]() |
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W[5] | Declaration | |
1942-06-05 | ![]() |
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W[11] | United States Declaration of War upon Hungary United States Declaration of War upon Romania United States declaration of war upon Bulgaria | |
1942-06-13 | ![]() |
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W | Having never made peace with Germany from the First World War, Haudenosaunee became the only Native American state to officially declare war on the Axis powers separately from the United States (other Native American nations issued declarations or declared war de facto alongside the United States as their tribal citizens enlisted in the Armed Forces). An Iroquois representative in full regalia announced on the steps of the U.S. Capitol by the following statement: "We represent the oldest, though smallest, democracy in the world today. It is the unanimous sentiment among Indian people that the atrocities of the Axis nations are violently repulsive to all sense of righteousness of our people, and that this merciless slaughter of mankind can no longer be tolerated. Now we do resolve that it is the sentiment of this council that the Six Nations of Indians declare that a state of war exists between our Confederacy of Six Nations on the one part and Germany, Italy, Japan and their allies against whom the United States has declared war, on the other part."[19] | Declaration |
1942-08-22 | ![]() |
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W | Declaration | |
1942-11-08 | ![]() ![]() |
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A | Invasion | |
1942-11-10 | ![]() ![]() |
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A | Invasion | |
1942-11-12 | ![]() |
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A | German invasion via airlifting several divisions in reaction to Operation Torch, swiftly occupying Tunis and the eastern part of the country, and capturing the western portions after French Tunisian resistance before the allies reached the Tunisian border. In the resulting Tunisian campaign, the Allies finally defeated the Axis forces in Africa. | Invasion |
1942-12-14 | ![]() |
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W | On 3 October 1935, Italy invaded Ethiopia without a formal declaration of war. In response to the Italian invasion, Ethiopia declared war on Italy. Most of Ethiopia was occupied by Italy in 1936, however parts of Ethiopia remained under the control of the Ethiopian Patriots Movement, which begun its guerrilla war against the occupying Italian forces the day Addis Ababa fell in May 1936. In May 1941, Addis Ababa was liberated by the Gideon Force, restoring sovereignty to Ethiopia. | Second Italo-Ethiopian War
Declaration |
1943-01-09 | ![]() |
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W[5] | Declaration | |
1943-01-17 | ![]() |
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W[5] | Declaration | |
1943-01-20 | ![]() |
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W | President Ríos officially suspended all trade and diplomatic relations with the Axis powers, and Chile officially joined the Allies as authorities began rooting out Nazi spies from Operation Bolivar. While only declaring war on Germany and Italy (although Chile would not declare war on Japan until 1945, it began imprisoning Japanese nationals in 1943), the American government and international press celebrated this day as Chile declaring war on the Axis. | Declaration |
1943-04-07 | ![]() |
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W | Bolivia officially joined the Allies on 7 April 1943. Shortly after war was declared, the President, Enrique Peñaranda, was overthrown in a coup. Bolivian mines supplied needed tin to the Allies, but no troops or warplanes were sent overseas. Bolivians remained confident their geographic isolation would protect them from the war. | Declaration |
1943-08-01 | ![]() |
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W[5] | Declaration | |
1943-09-08 | ![]() |
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A | After Italy's capitulation to the Allied powers, Germany swiftly invaded both Italy and Italian-controlled territories (such as Albania, an Italian satellite state) to preempt a possible Allied intervention. | Operation Achse, German occupation of Albania |
1943-09-09 | ![]() |
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W | Declaration | |
1943-10-13 | ![]() |
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W[3] | Italy had changed sides after the fall of Mussolini. The Declaration of War was given by Pietro Badoglio to the German ambassador in Madrid.[3] | Declaration |
1943-11-26 | ![]() |
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W | See Colombia during World War II | Declaration |
1944-01-17 | ![]() |
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A | Invasion | |
1944-01-27 | ![]() |
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W | Declaration | |
1944-06-06 | ![]() |
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A | Invasion | |
1944-07-25 | ![]() |
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A | Invasion | |
1944-08-25 | ![]() |
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W[5] | Romania switched sides | Declaration |
1944-09-05 | ![]() |
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W | Declaration | |
1944-09-07 | ![]() |
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W[5] | Declaration | |
1944-09-07 | ![]() |
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W[5] | Declaration | |
1944-09-08 | ![]() |
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W | Bulgaria switched sides | Declaration |
1944-09-15 | ![]() |
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A | Lapland War | |
1944-09-21 | ![]() |
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W[20] | Battle of San Marino | |
1944-09-23 | ![]() |
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W[21] | Philippine declaration | |
1944-12-28 | ![]() |
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W[22] | The Provisional National Government, which had been established under Soviet protection in the city of Debrecen, declared war on Germany. The German-backed Arrow Cross regime was still at war with the Soviet Union and its troops were still in action. As it had not switched sides of its own accord, Hungary was never recognized as having defected to the Allies. | Hungarian declaration |
1945-02-02 | ![]() |
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W | Ecuadorian declaration | |
1945-02-07 | ![]() |
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W | Paraguayan declaration | |
1945-02-12 | ![]() |
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W[5] | Declaration | |
1945-02-15 | ![]() ![]() |
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W |
Venezuelan declaration Uruguayan declaration | |
1945-02-23 | ![]() |
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W | Declaration | |
1945-02-24 | ![]() |
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W | Declaration | |
1945-02-26 | ![]() ![]() |
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W | Declaration | |
1945-02-28 | ![]() |
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W | Declaration | |
1945-03-01 | ![]() |
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W[5] | Declaration | |
1945-03-01 | ![]() |
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W[5] | Iran declares war on Japan retroactive to the previous day (Feb. 28, 1945) | Declaration |
1945-03-03 | ![]() |
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W | Finland declares war on Germany retroactive to Sept. 15, 1944 following terms of 1944 Moscow Armistice | Lapland War |
1945-03-07 | ![]() |
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W[5] | Declaration | |
1945-03-27 | ![]() |
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W |
Argentinean declaration | |
1945-04-11 | ![]() |
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W | Declaration | |
1945-06-07 | ![]() |
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W[5] | Declaration | |
1945-07-09 | ![]() |
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W | Norwegian government-in-exile announces that it had declared war on Japan on December 7, 1941 | Declaration[23] |
1945-07-14 | ![]() |
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W | Declaration | |
1945-08-08 | ![]() |
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W[3] | Last outbreak of war during the entire Second World War. | Soviet–Japanese War |
1945-08-10 | ![]() |
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W[24] | W (de jure) A (de facto 1945-08-09) War declared 24 hours after crossing the border with Soviet troops | |
1945-08-15 | ![]() |
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W | Viet Minh declared of war on Japanese government in Indochina on August Revolution | Vietnamese famine of 1945, Birth of the Viet Minh |