when did britain join the 2nd world war
British Empire in World War II On 1 September 1939, Germany invaded Poland. Two days later, on 3 September, after a British ultimatum to Germany to cease military operations was ignored, Britain and France declared war on Germany. Britain's declaration of war automatically committed India, the Crown colonies, and the protectorates, but the 1931 Statute of Westminster had granted autonomy to the Dominions so each decided their course separately.
Allies of World War II 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.[1] 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.