account of the break in 1927, see Roger Schinness, "The Conservative Party and Anglo-Soviet Relations, 1925–27", European History Quarterly 7, 4 (1977): 393–407. After the 1929 general election, the incoming Labour government of Ramsay MacDonald successfully established permanent diplomatic relations. Second World War In 1938, Britain and France negotiated the Munich Agreement with Nazi Germany. Stalin opposed the pact and refused to recognize the German annexation of the Czechoslovak Sudetenland. German-Soviet Non-aggression Pact 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.Francis Beckett, Enemy Within: The Rise And Fall of the British Communist Party (John Murray, 1995) 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. Anglo-Soviet alliance In June 1941, Germany launched Operation Barbarossa, attacking the USSR. Britain and the USSR agreed an alliance the following month with the Anglo-Soviet Agreement. The Anglo-Soviet invasion of Iran in August overthrew Reza Shah and secured the oil fields in Iran from falling into Axis hands. The Arctic convoys transported supplies between Britain and the USSR during the war. Britain was quick to provide limited materiel aid to the Soviet Union - including tanks and aircraft - via these convoys in order to try to keep her new ally in the war against Germany and her allies. One major conduit for supplies was through Iran. The two nations agreed on a joint occupation of Iran, to neutralize German influence. After the war, there were disputes about the Soviet delayed departure from Iran, and speculation that it planned to set up a puppet state along its border. That problem was resolved completely in 1946. The Soviet Union joined the Second Inter-Allied Meeting in London in September. The USSR thereafter became one of the "Big Three" Allies of World War II