Eventually a secret agreement with Nazi Germany allowed Germany and the Soviet Union to successfully invade and destroy the Second Republic in 1939. The following years of Soviet repressions of Polish citizens, especially the brutal mass murder in 1940, known as the Katyn massacre, of more than 20,000 Polish officers and its subsequent Soviet denial for 50 years, became additional events with lasting repercussions on the Polish–Russian relations. In 1944, the Polish Home Army timed their capital's uprising to coincide with the approaching Red Army on the eastern suburbs of the city and the retreat of German forces. However, the Red Army stopped at the city limits and remained inactive there for several weeks. Also, the Soviet Union did not allow its Western Allies to use its nearby airports for airdrops into Warsaw for several weeks. This allowed the German forces to regroup and demolish the city while defeating the Polish resistance and causing between 150,000 and 200,000 civilian deaths. The tragic circumstances under which Poland's capital was liberated further strained the Polish–Russian relations.