<Tr> <Td> Warsaw Pact </Td> <Td> </Td> </Tr> <P> The Allies of World War II, called the United Nations from the 1 January 1942 declaration, were the countries that together opposed the Axis powers during the Second World War (1939--1945). The Allies promoted the alliance as seeking to stop German, Japanese and Italian aggression . </P> <P> At the start of the war on 1 September 1939, the Allies consisted of France, Poland and the United Kingdom, and dependent states, such as the British India . Within days they were joined by the independent Dominions of the British Commonwealth: Australia, Canada, New Zealand and South Africa . After the start of the German invasion of North Europe till the Balkan Campaign, the Netherlands, Belgium, Greece and Yugoslavia joined the Allies . After first having cooperated with Germany in invading Poland whilst remaining neutral in the Allied - Axis conflict, the Soviet Union perforce joined the Allies in June 1941 after being invaded by Germany . The United States provided war materiel and money all along, and officially joined in December 1941 after the Japanese attack on Pearl Harbor . China had already been in a prolonged war with Japan since the Lugou Bridge Incident of 1937, but officially joined the Allies in 1941 . </P> <P> The alliance was formalised by the Declaration by United Nations, from 1 January 1942 . However, the name United Nations was rarely used to describe the Allies during the war . The leaders of the "Big Three"--the UK, the Soviet Union, and the United States--controlled Allied strategy; relations between the United Kingdom and the United States were especially close . China and the Big Three were referred as a "trusteeship of the powerful", then were recognized as the Allied "Big Four" in a Declaration by United Nations and later as the "Four Policemen" of the United Nations . </P>

When did the us join the allied powers