The USSR and Germany signed the Non-aggression Pact in late August 1939, which promised the Soviets control of about half of Eastern Europe, and removed the risk to Germany of a two front war. Germany invaded Poland on 1 September, and the Soviets followed sixteen days later. Many members of the Communist Party in Britain and sympathisers were outraged and quit. Those who remained strove to undermine the British war effort and campaigned for what the Party called a 'people's peace', i.e. a negotiated settlement with Hitler. Britain, along with France, declared war on Germany, but not the USSR. The British people were sympathetic to Finland in her Winter War against the USSR. The USSR furthermore supplied oil to the Germans which Hitler's Luftwaffe needed in its Blitz against Britain in 1940.