Declarations of war during World War II
This is a timeline of formal declaration 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 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. 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 outbreak of wars between nations which occurred during World War II. Indicated are the dates, from which a de facto state of war existed between nations. The table shows both the "Initiator Nation" and the nation at which the aggression was aimed, or "Targeted Nation". 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;
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 | Targeted nation | Declaration of war: Type | Notes/comments | Document/event |
| 1939-09-01 |  Germany | Poland | U | German attack began at 4:44 a.m., Berlin and Warsaw time. | Invasion |
| 1939-09-01 | Slovak Republic | Poland | A | Invasion | |
| 1939-09-03 | France  Transjordan Morocco Tunisia | Germany | 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 |
| 1939-09-04 | Germany | W | Declaration | ||
| 1939-09-05 | South Africa | Germany | W | Declaration | |
| 1939-09-10 | Bahrain Oman | Germany | W | Declaration Declaration Declaration | |
| 1939-09-17 | Poland | A | Invasion | ||
| 1939-11-09 |  Kuwait | Germany | W | Kuwaiti Declaration of War | |
| 1939-11-30 | A | Second war between these nations. | Invasion | ||
| 1940-04-09 | Germany | | A | Invasion of Denmark Invasion of Norway | |
| 1940-04-12 | United Kingdom | A | Invasion | ||
| 1940-05-10 | Germany | | A/W | Date of the German offensive in the West, W from Belgium and the Netherlands. | Belgium Netherlands |
| 1940-05-10 | Germany | A | Luxembourg | ||
| 1940-05-10 |  Iceland | A | Invasion | ||
| 1940-06-10 | Italy | France | W | France and the UK | |
| 1940-06-10 | Italy | W | Declaration | ||
| 1940-06-11 | South Africa | Italy | W | South Africa Australia New Zealand | |
| 1940-06-11 | France | Italy | W | Declaration | |
| 1940-06-25 | Vichy France | A | Vichy France cuts off diplomatic relations with the United Kingdom on 8 July 1940. | Attack | |
| 1940-09-09 | Italy | Egypt | A | Egypt never formally declared war on Italy. | Invasion |
| 1940-09-22 | Empire of Japan | Vichy France | A | Invasion | |
| 1940-09-23 | Free France | Vichy France | A | Invasion | |
| 1940-10-?? | Vichy France | A | Franco-Thai War | ||
| 1940-10-28 | Kingdom of Italy | Greece | U | Italy invades Greece | Invasion |
| 1941-02-05 | Free France | Italy | A | Invasion | |
| 1941-04-06 | Germany | Greece | W | Invasion | |
| 1941-04-06 | Germany | Yugoslavia | A | Invasion | |
| 1941-04-06 | Italy | Yugoslavia | A | Invasion | |
| 1941-04-07 | Yugoslavia | Hungary | A | 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 | Invasion | |
| 1941-06-22 | Germany Italy Romania | A | A timed-declaration of war was given by Germany at the time of the attack | Invasion | |
| 1941-06-22 | Tuva | Germany | 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 | ||
| 1941-06-27 | 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 | Invasion | |
| 1941-08-25 | | Iran | A | Invasion | |
| 1941-12-05 | Romania Hungary | W | Declaration | ||
| 1941-12-07 | Empire of Japan | | A | W ; A | Declaration Attack on Pearl Harbor Invasion of Malaya Attack on Singapore Invasion of Hong Kong |
| 1941-12-07 | | Empire of Japan Romania Hungary | W | Declaration | |
| 1941-12-07 | Empire of Japan | W | Declaration | ||
| 1941-12-08 | Commonwealth of the Philippines | Empire of Japan | W | United States declaration British declaration Australian declaration Costa Rican declaration Dominican Republic's declaration Guatemalan declaration Salvadorian declaration Haitian declaration Honduran declaration Dutch declaration New Zealand's declaration Nicaraguan declaration Philippine declaration | |
| 1941-12-08 | South Africa | Empire of Japan | W | South African declaration | |
| 1941-12-08 | Mongolia | Germany | W | Mongolian declaration | |
| 1941-12-08 | Romania Hungary | W | Declaration | ||
| 1941-12-09 | | Empire of Japan | W | Australian declaration New Zealand's declaration | |
| 1941-12-09 | Republic of China | Germany Italy Empire of Japan | W | China and Japan had been at undeclared war since 1937 | Second Sino-Japanese war Declaration |
| 1941-12-11 | Germany Italy | W | German declaration Italian declaration | ||
| 1941-12-11 | Germany Italy | W | Germany Italy | ||
| 1941-12-11 | Poland | Empire of 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 | | W | Romanian declaration Bulgarian declaration | |
| 1941-12-12 | | Portugal | A | Portugal maintained neutrality throughout World War II. | Invasion |
| 1941-12-13 | South Africa | Bulgaria | W | British declaration New Zealand's declaration South African declaration | |
| 1941-12-15 | Hungary | C | 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 if this act, the next day the Prime Minister in written reinforced it. | Declaration | |
| 1941-12-14 | Independent State of Croatia | | W | Declaration | |
| 1941-12-16 | Czechoslovakia | Germany Italy Romania Hungary Japan Bulgaria Independent State of Croatia | W | Declaration | |
| 1941-12-17 | Albania | W | Declaration | ||
| 1941-12-20 | Empire of Japan | W | Declaration | ||
| 1942-01-01 | United Nations | Axis Powers | W | Declared during Arcadia Conference | Declaration |
| 1942-01-06 | Bulgaria | W | Declaration | ||
| 1942-01-16 | Iraq | Germany Italy Empire of Japan | W | Declaration | |
| 1942-01-25 | | A | Declaration | ||
| 1942-01-25 | South Africa | W | British declaration New Zealand's declaration South African declaration | ||
| 1942-02-12 | Germany Empire of Japan | W | Declaration | ||
| 1942-02-19 | Empire of Japan | Portugal | A | Portugal maintained neutrality throughout World War II. | Invasion |
| 1942-05-05 | South Africa Netherlands Poland | Vichy France | A | Invasion | |
| 1942-05-05 | United Kingdom Northern Rhodesia Southern Rhodesia South Africa Tanganyika Belgian Congo | Vichy France Empire of Japan | A | Invasion | |
| 1942-05-22 | Germany Italy Empire of Japan | W | Declaration | ||
| 1942-06-05 | Hungary Romania Bulgaria | W | Declaration | ||
| 1942-06-13 | Iroquois Confederacy | Germany Italy Empire of Japan | 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 |
| 1942-08-22 | Brazil | Germany Italy | W | Declaration | |
| 1942-11-08 | United States Canada | Vichy France | A | Invasion | |
| 1942-11-10 | Germany Italy | Vichy France | A | Invasion | |
| 1942-11-12 | Germany | Tunisia | 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 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 | Ethiopia | Germany Italy Empire of Japan | 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 |
| 1943-01-20 | Germany Italy | 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, 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 | |
| 1943-09-01 | China Regime of Wang Jingwei | Allied Powers | W | Declaration | |
| 1943-09-09 | Iran | Germany | W | Declaration | |
| 1943-10-13 | Italy | Germany | 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 | Colombia | Germany | W | See Colombia during World War II | Declaration |
| 1944-01-17 | Free France | Italian Social Republic | A | Invasion | |
| 1944-01-27 | Liberia | Germany Empire of Japan | W | Declaration | |
| 1944-06-06 | France | Germany | A | Invasion | |
| 1944-07-25 | France | Empire of Japan | A | Invasion | |
| 1944-08-25 | Romania | Germany Hungary | W | Romania switched sides | Declaration |
| 1944-09-05 | Bulgaria | W | Declaration | ||
| 1944-09-08 | Bulgaria | Germany | W | Bulgaria switched sides | Declaration |
| 1944-09-15 | Germany | A | Lapland War | ||
| 1944-09-23 | | W | Philippine declaration | ||
| 1945-02-02 | Germany Empire of Japan | W | Ecuadorian declaration | ||
| 1945-02-07 | | Germany Empire of Japan | W | Argentinean declaration Paraguayan declaration | |
| 1945-02-15 | Venezuela | Germany Empire of Japan | W | Venezuelan declaration Uruguayan declaration | |
| 1945-02-21 | Germany | W | Declaration | ||
| 1945-02-23 | Germany Empire of Japan | W | Declaration | ||
| 1945-02-24 | Egypt | Germany Empire of Japan | W | Declaration | |
| 1945-02-26 | Syria | Germany Empire of Japan | W | Declaration | |
| 1945-02-28 | Germany | W | Declaration | ||
| 1945-03-03 | Germany | W | Finland switched sides | Lapland War | |
| 1945-04-01 | Empire of Japan | W | Declaration | ||
| 1945-04-11 | Japan | W | Declaration | ||
| 1945-07-06 | Brazil | Empire of Japan | W | Declaration | |
| 1945-07-09 | Empire of Japan | W | Declaration | ||
| 1945-07-14 | Italy | Empire of Japan | W | Declaration | |
| 1945-08-08 | Empire of Japan | W | Last outbreak of war during the entire Second World War. | Declaration | |
| 1945-08-10 | Mongolia | Empire of Japan | W | W A War declared 24 hours after crossing the border with Soviet troops | Soviet Invasion of Manchuria Mongolia in World War II |