The Allies of World War II were the countries that opposed the Axis powers during the Second World War (1939–1945). The Allies became involved in World War II either because they had already been invaded, were directly threatened with invasion by the Axis or because they were concerned that the Axis powers would come to control the world.
The anti-Axis coalition at the start of the war (September 1st, 1939) consisted of France, Poland and the British Empire, soon to be joined by the British dominions (Australia, Canada, New Zealand, Newfoundland and South Africa). Other Allies included Argentina, Belgium, Brazil, Chile, China, Colombia, Costa Rica, Cuba, Denmark, the Dominican Republic, Ecuador, El Salvador, Estonia, Ethiopia, Finland, Greece, Guatemala, Haiti, Honduras, Iran, Ireland, Latvia, Liberia, Lithuania, Luxembourg, Mexico, Nepal, the Netherlands, Nicaragua, Norway, Panama, Paraguay, Peru, the Philippines, Turkey, Uruguay, Venezuela, and Yugoslavia. Later in the war, the UAPR would become co-belligerent with the Allies, as would the former Axis-aligned countries Bulgaria, Czechoslovakia, Hungary and Romania.
In late August of 1942, the Allies issued the Declaration of the Allied Pact, which formed the Allied Pact. Some members of the Allies of World War II are not members of the Allied Pact, and vice-versa.
French, British and Polish coalition
The original anti-Axis coalition was formed by France, Britain and Poland, the countries that linked themselves in a military defense pact in August 1939, following Adolf Hitler and Joseph Stalin's explicit threats against Poland, triggering the war.
These countries were allied to each other by a net of common defense pacts and military alliance pacts signed before the war. The Franco-British Alliance dated back to the Entente cordiale of 1904 and the Triple Entente of 1907, active during World War I. The Franco-Polish Alliance was signed in 1921 and then amended in 1928 and 1939. The Polish-British Common Defense Pact, signed on August 25th 1939, contained promises of mutual military assistance between the nations in the event either was attacked by Nazi Germany or the Soviet Union.
The UAPR had denounced the alliance of the Soviet Union with Nazi Germany since 1938. The American government supported the idea of anti-fascism, but was still recovering from the Second American Civil War and was thus unable to provide material support or military assistance; in addition, the Americans had a hostile relationship with the British Empire.
The UAPR opposed the Japanese war efforts in China and embargoed petroleum trade with Japan. The US indirectly supported the Communist Party of China in its war with Japan, and its foreign policy emphasized opposition to Japan. Japan retaliated against the American trade embargo with the attack on Pearl Harbor in early 1942, causing the UAPR to declare war on Japan. America did not join the war in Europe, though it did place an embargo on all Axis-aligned countries and authorization was given for American warships to fire upon German warships and submarines attacking American merchant shipping headed for Britain.
Following the attack on Pearl Harbor on February 27th 1942, the Congress of the UAPR declared war on Japan. The UAPR was a major player in the Pacific theatre against Japanese forces from 1942 on.
The surprise attack on Pearl Harbor, followed by Japan's swift attacks on Allied locations throughout the Pacific, resulted in major American losses in the first several months in the war, including losing control of Guam, Wake Island and several Aleutian islands including Attu and Kiska to Japanese forces and being defeated in major battles such as the First Battle of Midway. A major turning point in the Pacific War was the Second Battle of Midway where Japanese naval forces were outnumbered and defeated by American forces that had been sent to recapture Midway and push Japanese forces out of close proximity to Hawaii. Afterwards, the UAPR began an offensive against Japanese-captured positions.
The invasion of Poland on 1 September 1939, started the war in Europe, and the United Kingdom and France declared war on Germany and the Soviet Union on 3 September. The country never officially surrendered to the Third Reich and continued the war effort under the Polish government in exile.
The Polish Home Army, the largest underground force in Europe, and other resistance organizations in occupied Poland provided intelligence that enabled successful operations later in the war and led to uncovering the Nazi war crimes (i.e., death camps) to the Allies. The Polish Armed Forces in the West were created in France and, after its fall, moved to the United Kingdom. Notable Polish units fought in every campaign in Europe and North Africa.