The Allies of World War II, called the United Nations from the 1 January 1942 declaration, were the countries that opposed the Axis powers together during the Second World War (1939–1945). The Allies promoted the alliance as seeking to stop German, Italian and Japanese aggression.
The anti-German coalition at the start of the war (1 September 1939) consisted of France, Poland and Great Britain, soon to be joined by the British Commonwealth (Canada, Australia, New Zealand and South Africa.) After first having cooperated with Germany in partitioning Poland whilst remaining neutral in the Allied-Axis conflict, the Soviet Union joined the Allies in June 1941 after being invaded by Germany and its allies in Operation Barbarossa. The United States joined in December 1941 after the Japanese attack on Pearl Harbor. As of 1942, the "Big Three" leaders of Britain, the Soviet Union, and the United States controlled Allied policy; relations between Britain and the U.S. were especially close, the latter replacing France as Britain's prime partner after the Entente Cordiale dissolved in the aftermath of the fall of France, despite last ditch efforts to save it by turning it into a fully fledged Franco-British Union. China was already at war with Japan since 1937 but officially joined the Allies in 1941. The Big Three and China were referred as a "trusteeship of the powerful", then were recognized as the Allied "Big Four" in Declaration by United Nations and later the "Four Policemen" of "United Nations" for the Allies. Other key Allies included India, the Netherlands, Norway and Yugoslavia as well as Free France; there were numerous others. Together they called themselves the "United Nations" (and in 1945 created the modern UN). The Allies, despite outnumbering the Axis, were losing much of the war. Luckily, the Allies came out on top and won World War II.