Declarations of war during World War II

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).On the Opening of Hostilities; 1907; Yale Law School Library; retrieved March 2014. For the diplomatic maneuvering behind these events, which led to hostilities between nations during World War II, see Diplomatic history of World War II.

List of war declarations Indicated in the table are the dates (during the preliminaries to, or during the course of, World War II), from which a de facto state of war existed between nations. The table shows 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 hostilities, 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.

+Outbreaks of war between nations during World War IIDateInitiator nation(s)Targeted nation(s)TypeNotes/commentsDocument/event1939-09-01 Germany Poland A German attack began at 4:44 a.m., Berlin and Warsaw time. Germany claimed that the attack was defensive, citing the Gleiwitz incident, which was actually a false flag attack. Invasion1939-09-01 Poland A Invasion1939-09-03 India Tonga Transjordan Germany U"2194 Days of War"; (1977); Salmaggi, C. & Pallasvini, A.; ; per tables included. [Italian; American] At 11:15 a.m. London time, British PM, Neville Chamberlain publicly delivered his Ultimatum Speech.1939: Britain and France declare war on Germany, BBC 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, instead, as part of the British Commonwealth (a protected state of the UK and the British Empire) declared war separately, alongside Britain (since it administers their foreign affairs). British declaration1939-09-03 France Morocco Tunisia Germany U The French ultimatum to Germany expired a few hours after the British ultimatum, at 17:00. French declaration1939-09-04 Nepal Germany W Declaration1939-09-06 South Africa Germany W Declaration1939-09-10 Bahrain Oman Germany W Canada's declaration several days after that of the United Kingdom is seen as a watershed moment in Canadian home rule and sovereignty.As for Bahrain, 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 declarationCanadian declarationMuscatian and Omanian declaration1939-09-17 Poland A Invasion1939-11-09 Kuwait Germany W Declaration1939-11-30 A Invasion1940-04-09 Germany A Invasion of DenmarkInvasion of Norway1940-04-12 United Kingdom A Invasion1940-05-10 Germany A/W Date of the German offensive in the West, W from Belgium, Luxemburg and the Netherlands.Swedish Encyklopedia; "Bonniers Lexikon" (Vol. 1); (c.1960s); table in article by Andra Världskriget: The Second World War; Pp. 461-462. BelgiumLuxembourgNetherlands1940-05-10 Iceland A Invasion1940-06-10 Italy France W Declaration1940-06-10 Italy W Declaration1940-06-11 South Africa France Italy W South African declarationAustralian declarationNew Zealand's declarationFrench declaration1940-07-03 Vichy France A Vichy France cuts off diplomatic relations with the United Kingdom on 8 July 1940. Attack1940-09-09 Italy Egypt A Egypt never formally declared war on Italy. Invasion1940-09-22 Vichy France A Japanese troops occupy French Indochina. Invasion1940-09-23 Free France Vichy France A Invasion1940-10-?? Vichy France A Franco-Thai War1940-10-28 Greece U Italy invades Greece. Invasion1940-10-27 Free France Vichy France AKennedy, David M. The Library of Congress World War II Companion p. 466 Free French Equatorial Africa invades Vichy French Gabon. Invasion1940-11-23 Belgium (in-exile) W Declaration1941-02-05 Free France Italy A Invasion1941-04-06 Germany Greece W Invasion1941-04-06 Germany Italy Yugoslavia A Invasion1941-04-07 Yugoslavia Hungary A After the German invasion, bombing of Hungarian locations. Invasion1941-04-14 Germany Egypt A Egypt did not formally declare war until 1945. Invasion1941-04-24 Bulgaria Greece Yugoslavia A Bulgaria declares war on Greece and Yugoslavia. Declaration1941-05-02 United Kingdom Iraq A Invasion1941-06-08 Free France Germany A Invasion1941-06-22 Germany Italy W A timed declaration of war was given by Germany and by Italy at the time of the attack."The Rise and Fall of the Third Reich"; Shirer, William L Invasion1941-06-22/24 Romania 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. The Romanian army began limited military operations. On June 24, Romania officially declared war on the Soviet Union. Declaration1941-06-22 Tuva Germany W Tuva was a client state of the Soviet Union. Part of the USSR from 1944. Declaration1941-06-25 W After the bombing of several Finnish locations, Finland recognized a state of war with the Soviet Union; third war between these nations. Continuation War1941-06-27 Hungary C 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. Invasion1941-08-25 Iran A Invasion1941-12-05 Romania Hungary W Declaration1941-12-06 Romania W Declaration1941-12-07 Hungary W UK declaration of war from 1941-12-05 entered into force on 1941-12-07 1 minute after midnight. Declaration1941-12-07 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.. "[The] fourteenth part was not a formal declaration of war. It did not even rupture diplomatic relations. It merely broke off the discussions." See . Declaration published after: Attack on Pearl Harbor Invasion of Hong Kong