Britain and France declared war on Germany, followed by Australia, New Zealand, South Africa, and Canada. During the Phoney War period, the alliance provided no direct military support to Poland, outside of a cautious French probe into the Saarland. The Western Allies also began a naval blockade of Germany, which aimed to damage the country's economy and the war effort. Germany responded by ordering U-boat warfare against Allied merchant and warships, which would later escalate into the Battle of the Atlantic. On 8 September, German troops reached the suburbs of Warsaw. The Polish counter offensive to the west halted the German advance for several days, but it was outflanked and encircled by the Wehrmacht. Remnants of the Polish army broke through to besieged Warsaw. On 17 September 1939, two days after signing a cease-fire with Japan, the Soviet Union invaded Poland under the pretext that the Polish state had ostensibly ceased to exist. On 27 September, the Warsaw garrison surrendered to the Germans, and the last large operational unit of the Polish Army surrendered on 6October. Despite the military defeat, Poland never surrendered; instead, it formed the Polish government-in-exile and a clandestine state apparatus remained in occupied Poland. A significant part of Polish military personnel evacuated to Romania and Latvia; many of them later fought against the Axis in other theatres of the war. Germany annexed the western and occupied the central part of Poland, and the Soviet Union annexed its eastern part; small shares of Polish territory were transferred to Lithuania and Slovakia. On 6 October, Hitler made a public peace overture to the United Kingdom and France but said that the future of Poland was to be determined exclusively by Germany and the Soviet Union. The proposal was rejected, and Hitler ordered an immediate offensive against France, which was postponed until the spring of 1940 due to bad weather. After the outbreak of war in Poland, Stalin threatened Estonia, Latvia, and Lithuania with military invasion, forcing the three Baltic countries to sign pacts that stipulated the creation of Soviet military bases in these countries. In October 1939, significant Soviet military contingents were moved there. Finland refused to sign a similar pact and rejected ceding part of its territory to the Soviet Union. The Soviet Union invaded Finland in November 1939, and the Soviet Union was expelled from the League of Nations. Despite overwhelming numerical superiority, Soviet military success