In 1918, following the outbreak of the Russian Revolution and the defeat of the Central Powers in World War I, Pilecki returned to Wilno (at that time part of the newly independent Polish Second Republic) and joined the ZHP section of the Lithuanian and Belarusian Self-Defense Militia, a paramilitary formation aligned with the White movement under General Władysław Wejtko. The militia disarmed the retreating German troops and took up positions to defend the city from a looming attack by the Soviet Red Army. However, Wilno fell to Bolshevik forces on 5 January 1919, and Pilecki and his unit resorted to partisan warfare behind Soviet lines. He and his comrades then retreated to Białystok where Pilecki enlisted as a "szeregowy" (private) in Poland's newly established volunteer army. He took part in the Polish-Soviet War of 1919–1921, serving under Captain Jerzy Dąbrowski. He fought in the Kiev Offensive (1920) and as part of a cavalry unit defending the city of Grodno. On 5 August 1920, Pilecki joined the 211th Uhlan Regiment and fought in the crucial Battle of Warsaw and in the Rudniki Forest ("Puszcza Rudnicka"). Pilecki later took part in the liberation of Wilno and briefly served in the ongoing Polish-Lithuanian War as a member of the October 1920 Żeligowski rebellion.