This is a timeline of formal 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 an act of delivering a performative speech (not to be confused with a mere 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).For the diplomatic maneuvering behind these events, which led to hostilities between nations during World War II, see the article entitled 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.
Table Legend: Concerning Declaration of War: A = Attack without prior, formal declaration of war; U = State of war arrived at through use of ultimatum;
W = Formal declaration of war made.
|Date||Initiator nation(s)||Targeted nation(s)||Declaration of war: Type||Notes/comments||Document/event|
|1939-09-01||U||German attack began at 4:44 a.m., Berlin and Warsaw time.||Invasion|
|1939-09-03||U||At 11:15 a.m. London time, British PM, Neville Chamberlain publicly delivered his Ultimatum Speech. 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 the following dominions.||United Kingdom declaration, French declaration|
|1939-09-05||W||As protectorates of France governed by resident-generals, hostilities between both Tunisia and Morocco and Germany fluctuated throughout the war. Initially declaring war and commiting forces under French command that participated in the 1940 campaign, the Armistice between Vichy and the Germans led to a suspending of hostilities. After Operation Torch, a state of war resumed between Morocco and Germany, which went on to employ large numbers of troops for the Allies. Tunisia was invaded by the Germans in response to Operation Torch.||Declaration|
|1939-11-30||A||Second war between these nations (after Finnish invasion in 1918-1920).||Invasion|
|1940-04-09||A|| Invasion of Denmark |
Invasion of Norway
|1940-05-10||A/W||Date of the German offensive in the West, W from Belgium and the Netherlands.|
|1940-06-10||W||France and the UK|
|1940-06-25||A||Vichy France cuts off diplomatic relations with the United Kingdom on 8 July 1940.||Attack|
|1940-09-09||A||Egypt never formally declared war on Italy.||Invasion|
|1940-10-28||U||Italy invades Greece||Invasion|
|1941-04-14||A||Egypt did not formally declare war until 1945.||Invasion|
|1941-06-22||A||A timed-declaration of war was given by Germany at the time of the attack||Invasion|
|W||Tuva was a client state of the Soviet Union. Part of the USSR from 1944.|
|1941-06-25||W||Finland recognized a state of war with the Soviet Union; third war between these nations.||Continuation War|
|1941-12-07||A||W (Japanese point of view); A (British Empire and United States)|
|1941-12-08||W|| United States declaration |
|1941-12-08||W||South African declaration|
|1941-12-08||W||China and Japan had been at war since 1937||Second Sino-Japanese war|
|1941-12-08||W[ citation needed ]|
|1941-12-11||W||Japan rejected declaration of War. Prime Minister Hideki Tōjō's answer was following: "We don't accept the Polish declaration of war. The Poles, fighting for their freedom, declared war under the British pressure".|
|1941-12-12||A||Portugal maintained neutrality throughout World War II.|
|1942-01-01||United Nations||Axis Powers||W||Declared during Arcadia Conference||Declaration|
|1942-02-19||A||Portugal maintained neutrality throughout World War II.||Invasion|
|1942-06-13||W||Only Native American tribe to have declared war on the Axis powers separately from the United States. Announced on the steps of the U.S. Capitol by a representative 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."||Declaration|
|1942-11-12||A||German invasion via airlifting serval divisions in reaction to Operation Torch, swiftly occupying Tunis and the eastern part of the country, and capturing the western portions after stiff 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||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|
|1943-01-20||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|
|1943-04-02||Axis powers||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|
|1943-09-08||A||After Italy's capitulation to the Allied powers, Germany swiftly invaded Albania (an Italian satellite state) to preempt a possible Allied intervention.||German occupation of Albania|
|1943-10-13||W||Italy had changed sides after the fall of Mussolini. The Declaration of War was given by Pietro Badoglio to the German ambassador in Madrid.||Declaration|
|1943-11-26||W||See Colombia during World War II||Declaration|
|1944-08-25||W||Romania switched sides||Declaration|
|1944-09-08||W||Bulgaria switched sides||Declaration|
|1944-12-31||W||Hungary switched sides||Declaration|
|1945-03-03||W||Finland switched sides||Lapland War|
|1945-08-08||W||Last outbreak of war during the entire Second World War.||Declaration|
|1945-08-10||W||W (de jure) A (de facto 1945-08-09) War declared 24 hours after crossing the border with Soviet troops|
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