Declarations of war during World War II

Animated map of the European Theater of war during WW II

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.

List of war declarations

Below is a table showing the Outbreaks 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.

Outbreaks of Wars between Nations during World War II Table Legend: Concerning "Declaration of War: Type." 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	Germany	Poland	A	German attack began at 4:44 am	Invasion
1939-09-03	United Kingdom, France	Germany	U	At 11 O'clock (am) British PM, Neville Chamberlain publicly delivered his Ultimatum Speech.	Document
1939-09-03	Australia, New Zealand	Germany	W		Australia New Zealand
1939-09-06	South Africa	Germany	W		Declaration
1939-09-10	Canada	Germany	W		Declaration
1939-09-17	Soviet Union	Poland	A		Invasion
1939-11-30	Soviet Union	Finland	A	First war between these nations.	Invasion
1940-04-09	Germany	Denmark, Norway	A		Invasion
1940-05-10	Germany	Belgium, Netherlands	A/W	Date of the German offensive in the West, W from Belgium and the Netherlands.	Belgium Netherlands
1940-05-10	Germany	Luxembourg	A		Luxembourg
1940-05-10	United Kingdom	Iceland	A		Invasion
1940-06-10	Italy	France, United Kingdom	W		France and the UK
1940-06-10	Canada	Italy	W		Declaration
1940-06-11	South Africa, Australia, New Zealand	Italy	W		South Africa Australia New Zealand
1940-06-11	France	Italy			Declaration
1940-10-28	Italy	Greece	U	Italy invades Greece	Invasion
1941-04-06	Germany	Greece	W		Invasion
1941-04-06	Germany, Bulgaria	Yugoslavia	A		Invasion
1941-04-06	Italy, Hungary	Yugoslavia	A		Invasion
1941-06-22	Germany, Italy, Romania	Soviet Union	A	A timed-declaration of war was given by Germany at the time of the attack	Invasion
1941-06-25	Finland	Soviet Union	W	Finland recognized a state of war with the Soviet Union; second war between these nations.	Continuation War
1941-06-27	Hungary	Soviet Union	W		Invasion
1941-12-06	United Kingdom	Finland	U		Declaration
1941-12-07	United Kingdom	Romania, Hungary	U		Declaration
1941-12-07	Empire of Japan	United States and the British Empire	A	W (Japanese point of view); A The "Western" (Attack on Pearl Harbor);	Declaration Attack on Pearl Harbor Invasion of Malaya Attack on Singapore Invasion of Hong Kong
1941-12-07	Canada, Australia, New Zealand	Japan, Finland, Romania, Hungary	W		Canada Australia New Zealand
1941-12-07	United Kingdom	Romania, Finland and Hungary	W		Declaration
1941-12-07	Panama	Japan	W		Declaration
1941-12-08	United States, United Kingdom, Australia, Philippines, Costa Rica, Dominican Republic, El Salvador,Guatemala, Haiti, Honduras, The Netherlands, New Zealand and Nicaragua	Japan, Germany	W		American declaration British declaration Australian declaration Cost Rican declaration Dominican Republic's declaration Salvadorian declaration Haitian declaration Honduran declaration Dutch declaration New Zealand's declaration Nicaraguan declaration Philippine declaration
1941-12-08	South Africa	Japan	W		South African declaration
1941-12-08	China	Germany, Italy, Japan	W	China and Japan had been at war since 1937	Second Sino-Japanese war Declaration
1941-12-09	Australia, New Zealand	Japan	W		Australian declaration New Zealand's declaration
1941-12-11	Germany, Italy	United States	W		German declaration Italian declaration
1941-12-11	United States	Germany, Italy	W		Germany Italy
1941-12-11	Poland's government-in-exile	Japan	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	Romania, Bulgaria	United States, United Kingdom	W		Romanian declaration Bulgarian declaration
1941-12-13	United Kingdom, New Zealand, South Africa	Bulgaria	W		British declaration New Zealand's declaration South African declaration
1941-12-13	Hungary	United States	W		Declaration
1941-12-14	Croatia	United States, United Kingdom	W		Declaration
1941-12-16	Czechoslovak government-in-exile	all countries at war with the United States, United Kingdom, or the Soviet Union	W		Declaration
1941-12-17	Albania	United States	W		Declaration
1941-12-19	Nicaragua	Bulgaria, Hungary and Romania	W		Declaration
1941-12-20	Belgium	Japan	W		Declaration
1942-01-01	United Nations	Axis powers	W	Declared during Arcadia Conference	Declaration
1942-01-06	Australia	Bulgaria	W		Declaration
1942-01-25	United Kingdom, New Zealand, South Africa	Thailand	W		British declaration New Zealand's declaration South African declaration
1942-05-22	Mexico	Germany, Italy, Japan	W		Declaration
1942-08-22	Brazil	Germany, Italy	W		Declaration
1943-04-02	Bolivia	Axis members	W		Declaration
1943-09-09	Iran	Germany	W		Declaration
1943-10-13	Italy	Germany	W	Italy had changed side after the fall of Mussolini. The Declaration of War was given by Pietro Badoglio to the German ambassador in Madrid.	Declaration
1944-08-25	Romania	Germany, Hungary	W	Romania switched sides	Declaration
1944-09-05	Soviet Union	Bulgaria	W		Declaration
1944-09-08	Bulgaria	Germany	W	Bulgaria switched sides	Declaration
1945-02-02	Ecuador	Germany, Japan	W		Ecuadorian declaration
1945-02-07	Argentina, Paraguay	Germany, Japan	W		Argentinean declaration Paraguayan declaration
1945-02-12	Peru	Germany, Japan	W		Declaration
1945-02-15	Venezuela, Uruguay	Germany, Japan	W		Venezuelan declaration Uruguayan declaration
1945-02-21	San Marino	Germany	W		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
1945-04-01	Saudi Arabia	Japan	W		Declaration
1945-04-03	Finland	Germany	W	Finland switched sides	Lapland War
1945-04-11	Chile	Japan	W		Declaration
1945-07-06	Brazil	Japan	W		Declaration
1945-07-14	Italy	Japan	W		Declaration
1945-08-08	Soviet Union	Japan	W	Last outbreak of war during the entire Second World War.	Declaration

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  Common parade of German Wehrmacht and Soviet Red Army on September 23, 1939 in Brest, Eastern Poland at the end of the Poland Campaign. In the center is Major General Heinz Guderian; and on the right is Brigadier General Semyon Krivoshein.

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  German paratroopers taking the Greek island of Crete, May 1941.

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  Photograph from a Japanese plane of Battleship Row at the beginning of the surprise Attack on Pearl Harbor. The explosion in the center is a torpedo strike on the USS Oklahoma. Two attacking Japanese planes can be seen: one over the USS Neosho and one over the Naval Yard.