This is a timeline ofdeclarations of war during World War II.
Adeclaration of war is a formal act by which one nation goes to war against another. The declaration is usually the act of delivering aperformative speech or the presentation of a signed document by an authorized party of a national government in order to create astate of war between two or more sovereign states. The official international protocol for declaring war was defined inThe Hague Peace Conference of 1907 (or Hague II).[1] For the diplomatic maneuvering behind these events, which led to hostilities between nations duringWorld War II, seeDiplomatic 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 ade 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 acasus belli thusfait 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 |
|---|---|---|---|---|---|
| 1939-09-01 |  Germany |  Poland | A | German attack began at 4:44 a.m., Berlin and Warsaw time.[2][better source needed][3][4] Germany claimed that the attack was defensive, citing theGleiwitz incident, which was actually afalse flag attack.[5] | Invasion |
| 1939-09-01 |  Slovakia | Poland | A | Invasion | |
| 1939-09-03 |  United Kingdom Australia New Zealand India Southern Rhodesia Tonga Transjordan | Germany | U[3][6] | At 11:15 a.m. London time,[7] British PM,Neville Chamberlain publicly delivered hisUltimatum Speech.[a][6][8] As theStatute 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 thosedominions.Tonga was not a British dominion, instead, as part of theBritish Commonwealth (aprotected state of the UK and theBritish Empire) declared war separately, alongside Britain (since it administers theirforeign affairs).[9] | British declaration |
| 1939-09-03 |  France Morocco Tunisia | Germany | U | The French ultimatum to Germany expired a few hours after the British ultimatum, at 17:00. | French declaration |
| 1939-09-04 |  Nepal | Germany | W | Declaration | |
| 1939-09-06 |  South Africa | Germany | W[3][6] | Declaration | |
| 1939-09-10 |  Bahrain Canada Oman | Germany | W[3][6] | Canada's declaration several days after that of the United Kingdom is seen as a watershed moment in Canadianhome rule and sovereignty. As forBahrain, given its status as a protected state of the United Kingdom, it was technically at war as of Britain's declaration, this is an acknowledgement of the declaration of war by Britain (due to coercion by an advisor), Oman, under British influence, is coerced to participate in the war effort. | Bahrainian declaration Canadian declaration Muscatian and Omanian declaration |
| 1939-09-17 |  Soviet Union | Poland | A[3][6] | Invasion | |
| 1939-11-09 |  Kuwait | Germany | W | Declaration | |
| 1939-11-30 | Soviet Union |  Finland | A[3][6] | Invasion | |
| 1940-04-09 | Germany |  Denmark Norway | A[3] | Invasion of Denmark Invasion of Norway | |
| 1940-04-12 | United Kingdom |  Faroe Islands | A[6] | Invasion | |
| 1940-05-10 | Germany |  Belgium Luxembourg Netherlands | A/W[3][6] | Date of the German offensive in the West, W from Belgium, Luxemburg and the Netherlands.[10] | Belgium Luxembourg Netherlands |
| 1940-05-10 | United Kingdom |  Iceland | A | Invasion | |
| 1940-06-10 |  Italy | FranceUnited Kingdom | W[3][6] | Declaration | |
| 1940-06-10 | Canada | Italy | W[3] | Declaration | |
| 1940-06-11 | South AfricaAustraliaNew ZealandFrance | Italy | W[3] | South African declaration Australian declaration New Zealand's declaration French declaration | |
| 1940-07-03 | United Kingdom |  Vichy France | A | Vichy France cuts off diplomatic relations with theUnited Kingdom on 8 July 1940. | Attack |
| 1940-09-09 | Italy |  Egypt | A | Egypt never formally declared war on Italy. | Invasion |
| 1940-09-22 |  Japan | Vichy France | A | Japanese troops occupy French Indochina. | Invasion |
| 1940-09-23 |  Free FranceUnited KingdomAustralia | Vichy France | A | Invasion | |
| 1940-10-?? |  Thailand | Vichy France | A | Franco-Thai War | |
| 1940-10-28 | Italy |  Greece | U[6] | Italy invades Greece. | Invasion |
| 1940-10-27 | Free France | Vichy France | A[11] | FreeFrench Equatorial Africa invades VichyFrench Gabon. | Invasion |
| 1940-11-23 | Belgium (in-exile) | Italy | W[12] | Declaration | |
| 1941-02-05 | Free France | Italy | A | Invasion | |
| 1941-04-06 | Germany | Greece | W[3][6] | Invasion | |
| 1941-04-06 | GermanyItaly |  Yugoslavia | A[3][6] | Invasion | |
| 1941-04-07 | Yugoslavia |  Hungary | A[13] | After the German invasion, bombing of Hungarian locations. | Invasion |
| 1941-04-14 | Germany | Egypt | A | Egypt did not formally declare war until 1945. | Invasion |
| 1941-05-02 | United Kingdom |  Iraq | A | Invasion | |
| 1941-06-08 | Free France | Germany | A | [citation needed] | Invasion |
| 1941-06-22 | GermanyItaly | Soviet Union | W[6] | A timeddeclaration of war was given by Germany at the time of the attack.[14] | Invasion |
| 1941-06-22/24 |  Romania | Soviet Union | A | On June 22, Romanian leader Ion Antonescu declared a "holy war" to reclaim ancestral lands and against Bolshevism in an appeal to the nation.[15] The Romanian army began limited military operations. On June 24, Romania officially declared war on the Soviet Union.[15] | Declaration |
| 1941-06-22 | .svg) Tuva | Germany | W | Tuva was a client state of the Soviet Union. Part of the USSR from 1944. | Declaration |
| 1941-06-24 |  Bulgaria | GreeceYugoslavia | A[6] | Bulgaria declares war on Greece and Yugoslavia. | Declaration |
| 1941-06-25 | Finland | Soviet Union | W | After the bombing of several Finnish locations,Finland recognized a state of war with theSoviet Union; third war between these nations. | Continuation War |
| 1941-06-27 | Hungary | Soviet Union | C[13] | 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 | Soviet UnionUnited KingdomAustralia |  Iran | A | Invasion | |
| 1941-12-05 | United KingdomIndia | FinlandRomaniaHungary | W[16] | Declaration | |
| 1941-12-06 | FinlandRomania | United Kingdom | W[6] | Declaration | |
| 1941-12-07 | United Kingdom | Hungary | W[17] | UK declaration of war from 1941-12-05 entered into force on 1941-12-07 1 minute after midnight. | Declaration |
| 1941-12-07 | Japan |  United StatesUnited KingdomThailand | 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.[18] SeeAttack on Pearl Harbor § Japanese declaration of war. | Declaration published after: |
| 1941-12-07 | CanadaAustraliaNew Zealand | FinlandRomaniaHungary | W[6] | Declaration | |
| 1941-12-07 |  PanamaYugoslavia (in-exile) | Japan | W[6] | Declaration | |
| 1941-12-08 | United KingdomUnited StatesCanadaAustralia Costa Rica Dominican Republic El SalvadorFree FranceGreece (in-exile) Haiti HondurasNetherlands (in-exile)New Zealand Nicaragua PhilippinesTonga[9] | Japan | W[6] | After theattack on Pearl Harbor, many countries declared a formal state of war on Japan. | British declaration United States declaration Canadian declaration Australian declaration Costa Rican declaration Dominican Republic's declaration Salvadoran declaration Haitian declaration Honduran declaration Dutch declaration New Zealand's declaration Nicaraguan declaration Philippine declaration Tongan declaration |
| 1941-12-08 | South Africa | JapanFinlandRomaniaHungary | W[6] | Declaration | |
| 1941-12-08 |  Mongolia | Germany | W[citation needed] | Declaration | |
| 1941-12-08 |  Manchukuo | United States | W[6] | Declaration | |
| 1941-12-08 | Japan | British Malaya | A | Invasion of Malaya Attack on Singapore | |
| 1941-12-09 |  Cuba Guatemala | Japan | W[6] | Cuban declaration Guatemalan declaration | |
| 1941-12-09 |  China | GermanyItaly Japan | W[6] | China and Japan had been atundeclared war since 1937. | Second Sino-Japanese war Declaration |
| 1941-12-10 |  Korea (government in exile)[19] | Japan | W | Many Korean armies such as theKorean Liberation Army had already been fighting Japan in theSecond Sino-Japanese war, although a formal declaration was not made until the attack on Pearl Harbor. | Declaration |
| 1941-12-11 | GermanyItaly | United States | W[3][6] | German declaration Italian declaration | |
| 1941-12-11 | United StatesCubaCosta RicaDominican RepublicGuatemalaNicaragua | GermanyItaly | W[6] | United States declaration of war on Germany (1941) United States declaration of war on Italy | |
| 1941-12-11 | Netherlands (in-exile) | Italy | W[6] | Declaration | |
| 1941-12-11 | Poland (in-exile) | Japan | W[3] | Japan rejected the 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].[b] | Declaration |
| 1941-12-12 | RomaniaBulgaria Slovakia | United StatesUnited Kingdom | W[6] | Romanian declaration Bulgarian declaration | |
| 1941-12-12 | HaitiEl SalvadorPanama | GermanyItaly | W[6] | Declaration | |
| 1941-12-12 | AustraliaNetherlands |  Portugal | A | Portugal maintained neutrality throughout World War II. | Invasion |
| 1941-12-13 | United KingdomNew ZealandSouth Africa | Bulgaria | W[6] | British declaration New Zealand's declaration South African declaration | |
| 1941-12-13 | Honduras | GermanyItaly | W[6] | Declaration | |
| 1941-12-13 | Italy | CubaGuatemala | W[6] | Declaration | |
| 1941-12-14 |  Independent State of Croatia | United StatesUnited Kingdom | W[6] | Declaration | |
| 1941-12-15 | Hungary | United States | C[20] | 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 |  Czechoslovakia (in-exile) | GermanyItalyFinlandRomaniaHungaryJapanBulgariaIndependent State of Croatia Slovakia | W[6] | 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 | Japan |  Sarawak North Borneo Brunei | A | Invasion | |
| 1941-12-17 |  Albania | United States | W | Declaration | |
| 1941-12-19 | Nicaragua | RomaniaHungaryBulgaria | W[6] | Declaration | |
| 1941-12-19 | Romania | Nicaragua | W[21] | Out of theAxis countries only Romania reciprocated, declaring war on Nicaragua on the same day. | Declaration |
| 1941-12-20 | Belgium (in-exile) | Japan | W | Declaration | |
| 1941-12-24 | Haiti | RomaniaHungaryBulgaria | W[6] | Declaration | |
| 1941-12-24 | Romania | Haiti | W[22] | Out of theAxis countries only Romania reciprocated, declaring war on Haiti on the same day. | Declaration |
| 1941-12-25 | Greece (in-exile) | Japan | W | Declaration | |
| 1942-01-01 | United Nations | Axis Powers | W | Declared duringArcadia Conference. | Declaration |
| 1942-01-06 | Australia | Bulgaria | W | Declaration | |
| 1942-01-25 | Thailand | United KingdomUnited States | A | Declaration | |
| 1942-01-25 | United KingdomNew ZealandSouth Africa | Thailand | W | British declaration New Zealand's declaration South African declaration | |
| 1942-02-19 | Japan | Portugal | A | Portugal maintained neutrality throughout World War II. | Invasion |
| 1942-03-02 | Australia | Thailand | W[6] | Declaration | |
| 1942-05-05 | South AfricaNetherlands (in-exile)Poland | Vichy France | A | Invasion | |
| 1942-05-05 | United Kingdom Northern RhodesiaSouthern RhodesiaSouth Africa Tanganyika Belgian Congo | Vichy France Japan | A | Invasion | |
| 1942-05-22 |  Mexico | GermanyItaly Japan | W[6] | Declaration | |
| 1942-06-05 | United States | HungaryRomaniaBulgaria | W[13] | Declaration of War on Hungary Declaration of War on Romania Declaration of war on Bulgaria | |
| 1942-06-13 | Iroquois Confederacy | GermanyItaly Japan | W | Having never made peace with Germany from theFirst 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 warde facto alongside the United States as their tribal citizens enlisted in the Armed Forces[23]). | |
| 1942-08-22 |  Brazil | GermanyItaly | W | Declaration | |
| 1942-11-08 | United StatesCanada | Vichy France | A | Invasion | |
| 1942-11-10 | GermanyItaly | Vichy France | A | Invasion | |
| 1942-11-12 | Germany | Tunisia | A | German invasion via airlifting several divisions in reaction toOperation 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 resultingTunisian campaign, the Allies finally defeated the Axis forces in Africa. | Invasion |
| 1942-12-14 |  Ethiopia | GermanyItaly Japan | W | On 3 October 1935,ItalyinvadedEthiopia 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 dayAddis Ababa fell in May 1936. In May 1941, Addis Ababa was liberated by theGideon Force, restoring sovereignty to Ethiopia. | Second Italo-Ethiopian War Declaration |
| 1943-01-09 |  Reorganized National Government of China | United StatesUnited Kingdom | W[6] | Declaration | |
| 1943-01-17 | Iraq | GermanyItaly Japan | W[6] | Declaration | |
| 1943-04-07 |  Bolivia | Axis powers | W[6] | Bolivia officially joined the Allies on 7 April 1943. Shortly after war was declared, thePresident,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 |  State of Burma | United StatesUnited Kingdom | W[6] | Declaration | |
| 1943-09-08 | Germany | ItalyAlbania | A | After Italy'scapitulation 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 | Iran | Germany | W | Declaration | |
| 1943-10-13 | Italy | Germany | W[3] | Italy had changed sides after the fall of Mussolini. The Declaration of War was given byPietro Badoglio to the German ambassador inMadrid.[3] | Declaration |
| 1943-11-26 |  Colombia | Germany | W | SeeColombia during World War II. | Declaration |
| 1944-01-17 | Free France |  Italian Social Republic | A | Invasion | |
| 1944-01-27 |  Liberia | Germany Japan | W | Declaration | |
| 1944-06-06 | France | Germany | A | Invasion | |
| 1944-07-25 | France | Japan | A | Invasion | |
| 1944-08-25 | Romania | Germany | W[6] | Romania switched sides. | Declaration |
| 1944-09-05 | Soviet Union | Bulgaria | W | Declaration | |
| 1944-09-07 | Hungary | Romania | W[6] | Declaration | |
| 1944-09-07 | Romania | Hungary | W[6] | Declaration | |
| 1944-09-08 | Bulgaria | Germany | W[citation needed] | Bulgaria switched sides. | Declaration |
| 1944-09-15 | Germany | Finland | A | Lapland War | |
| 1944-09-23 |  Second Philippine Republic | United StatesUnited Kingdom | W[24] | Declaration | |
| 1944-12-28 | Hungary | Germany | W[25] | TheProvisional National Government [ru], which had been established under Soviet protection in the city of Debrecen, declared war on Germany. The German-backedArrow Cross regime was still at war with the Soviet Union and its troops were still in action. In January 1945, the Provisional National Government signed an armistice with the Allies, where it confirmed the declaration of war on Germany and obliged itself to form military forces loyal to the Allies.[26] | Declaration |
| 1945-02-02 |  Ecuador | Germany Japan | W | Declaration | |
| 1945-02-07 |  Paraguay | Germany Japan | W | Declaration | |
| 1945-02-12 |  Peru | Germany Japan | W[6] | Declaration | |
| 1945-02-15 |  Venezuela Uruguay | Germany Japan | W | Venezuelan declaration Uruguayan declaration | |
| 1945-02-23 |  Turkey | Germany Japan | W | Declaration | |
| 1945-02-24 | Egypt | Germany Japan | W | Declaration | |
| 1945-02-26 |  Syria Lebanon | Germany Japan | W | Declaration | |
| 1945-02-28 |  Saudi Arabia | Germany | W | Declaration | |
| 1945-03-01 | Saudi Arabia | Japan | W[6] | Declaration | |
| 1945-03-01 | Iran | Japan | W[6] | Iran declared war on Japan retroactive to the previous day (Feb. 28, 1945). | Declaration |
| 1945-03-03 | Finland | Germany | W | Finland declared war on Germany retroactive to Sept. 15, 1944 following terms of 1944Moscow Armistice. | Lapland War |
| 1945-03-07 | Romania | Japan | W[6] | Declaration | |
| 1945-03-27 |  Argentina | Germany Japan | W | Declaration | |
| 1945-04-11 |  Chile | Japan | W | Chile cut off diplomatic relations with theGermany,Italy andJapan on 20 January 1943. | Declaration |
| 1945-06-07 | Brazil | Japan | W[6] | Declaration | |
| 1945-07-09 | Norway (in-exile) | Japan | W | Norwegian government-in-exile announced that it had declared war on Japan on December 7, 1941. | Declaration[27] |
| 1945-07-14 | Italy | Japan | W | Declaration | |
| 1945-08-08 | Soviet Union | Japan | W[3] | Last outbreak of war of the Second World War. | Soviet–Japanese War |
| 1945-08-10 |  Mongolia | Japan | W[28] | W (de jure) A (de facto 1945-08-09) War declared 24 hours after crossing the border with Soviet troops. | Soviet Invasion of Manchuria Mongolia in World War II |
