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.