A thaw in Polish–Lithuanian relations began in spring 1939. After the German–Czech and German–Lithuanian crises, Poland made more active efforts to ensure Lithuania's assistance, or at least neutrality, in the event of a war with Nazi Germany. Lithuanian General Stasys Raštikis and Polish Foreign Minister Józef Beck made high-profile visits to each other's countries, and Poland improved the conditions of Lithuanians in the Vilnius Region. However, Lithuania did not believe that Poland and its western allies were strong enough to resist Germany and the Soviet Union. When Germany invaded Poland in September 1939, Lithuania maintained a policy of strict neutrality, refusing repeated German offers for a joint attack on Poland to capture Vilnius. Instead, Lithuania interned about 15,000 Polish soldiers and accepted about 35,000 Polish civilian refugees. The Soviet Union returned Vilnius to Lithuania after the Soviet invasion of Eastern Poland in September 1939. Neither country was aware at the time of the secret protocols of the Molotov–Ribbentrop Pact, signed in August 1939, in which Germany and the Soviet Union agreed to divide the region into their spheres of influence. In June 1940, the Soviet Union occupied and annexed Lithuania in accordance with the Molotov–Ribbentrop Pact. A year later Russia was attacked by Nazi Germany leading to the Nazi occupation of Lithuania.