<P> 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 . </P>
when did the united kingdom entered world war 2
1939