"Nevertheless, from November 1918 onwards the tide of the civil war ran the Bolsheviks' way. By April 1919 Kolchak's forces had been beaten and by July Perm was back in Bolshevik hands, followed by Omsk itself in November. Denikin enjoyed some success in the Ukraine in the summer of 1919 but had lost Kiev by the end of the year. Yudenich's attempt to capture Petrograd had also failed, thanks in large measure to Trotsky's rallying of the city's defenders, who drove the defeated White army back into Estonia, whence they had come. General Peter Wràngel's Caucasian Army had captured Tsaritsyn that June, but by January 1920 it was clear that the war was effectively over. The Allies cut off their aid to the Whites. One by one the generals fled or, like Kolchak, were captured and executed. By the summer of 1920 Lenin felt confident enough to export the Revolution westwards, ordering the Red Army to march on Warsaw and confidently talking of the need to 'sovietize Hungary and perhaps Czechia and Romania too'. Only their decisive defeat by the Polish army on the banks of the River Vistula halted the spread of the Bolshevik epidemic."