The Polish –Soviet War ( February 1919 – March 1921) was an armed conflict between the Second Polish Republic, the Ukrainian People 's Republic, Soviet Russia and Soviet Ukraine over the control of an area equivalent to today's western Ukraine and parts of modern- day Belarus.
Although united under communist leadership, Soviet Russia and Soviet Ukraine were theoretically two separate independent entities because the Soviet republics did not unite into the Soviet Union until 1922.
Poland 's Chief of State, Józef Piłsudski, felt the time was right to expand Polish borders as far east as feasible, to be followed by a Polish -led Intermarium federation of Central and Eastern European states as a bulwark against the re-emergence of German and Russian imperialism. Lenin, meanwhile, saw Poland as the bridge the Red Army had to cross to assist other communist movements and bring about other European revolutions. By 1919, Polish forces had taken control of much of Western Ukraine, emerging victorious from the Polish –Ukrainian War. The West Ukrainian People 's Republic, led by Yevhen Petrushevych, had tried to create a Ukrainian state on territories to which both Poles and Ukrainians laid claim. At the same time in the Russian part of Ukraine Symon Petliura tried to defend and strengthen the Ukrainian People 's Republic, but as the Bolsheviks began to gain the upper hand in the Russian Civil War, they started to advance westward towards the disputed Ukrainian territories, causing Petliura's forces to retreat to Podolia. By the end of 1919, a clear front had formed as Petliura decided to ally with Piłsudski. Border skirmishes escalated following Piłsudski's Kiev Offensive in April 1920. The Polish offensive was met by an initially successful Red Army counterattack.
