After the German Ober Ost garrisons were withdrawn from the Eastern Front following the Armistice, both Soviet Russian armies and Polish ones moved in to fill the vacuum. The newly independent Polish state and the Soviet government each sought territorial expansion in the region. Polish and Russian troops first clashed in February 1919, with the conflict developing into the Polish–Soviet War. Unlike the Soviets' previous conflicts, this had greater implications for the export of revolution and the future of Europe. Polish forces pushed into Ukraine and by May 1920 had taken Kiev from the Soviets. After forcing the Polish Army back, Lenin urged the Red Army to invade Poland itself, believing that the Polish proletariat would rise up to support the Russian troops and thus spark European revolution. Trotsky and other Bolsheviks were sceptical, but agreed to the invasion. The Polish proletariat did not rise, and the Red Army was defeated at the Battle of Warsaw. The Polish armies pushed the Red Army back into Russia, forcing Sovnarkom to sue for peace; the war culminated in the Peace of Riga, in which Russia ceded territory to Poland.