Their aim was to defeat the pro-communist Vilna Soviet of Workers Deputies, a rival faction within Vilnius seeking to govern the city.

[1] One of Piłsudski's objectives was to take control of Vilnius before Western diplomats at the Paris Peace Conference could rule on whom the city, demanded by various factions, should be given to.

[17] By early April, when members of the Kresy Defence Committee (Komitet Obrony Kresów) Michał Pius Römer, Aleksander Prystor, Witold Abramowicz, and Kazimierz Świtalski met with Pilsudski, stressing the plight of occupied Vilnius and its inhabitants' need for self-government, Piłsudski was ready to move.

[2] The forces moving on Vilnius included the cavalry group of Colonel Wladyslaw Belina-Prazmowski, composed of 800 men in nine cavalry squadrons and a battery of horse artillery; and infantry under General Edward Rydz-Śmigły, composed of 2,500 men in three battalions of the Polish 1st Legions Infantry Division and two batteries of heavy artillery.

[1] Cavalrymen fought for control of the center of Vilnius and took Cathedral Square,[21] the castle complex on the hillside, and the enemy quarters on the southern riverbank.

They also captured hundreds of Bolshevik soldiers and officials,[1] but their numbers were too small compared to the enemy forces, who had begun to reorganize, particularly in the north and west of the town, and to prepare a counterattack.

[17] By the evening of 19 April half of Vilnius was under Polish control,[20] however, the Red Army troops and supporters were putting up a stubborn and coordinated defence.

[17] Only upon the arrival of the main force of Polish infantry under Generał Śmigły on 21 April did the Poles gain the upper hand, attacking those parts of the town still held by the Red Army.

[20] As the Polish troops entered the city, the first pogrom in modern Vilnius started, as noted by the Timothy D. Snyder, citing Michał Pius Römer.

[22] Dozens of people connected with the Lit-Bel were arrested, and some were executed; Norman Davies cites a death toll for all – Jews and non-Jews, under Polish rule – as 65.

[3][25][28] The US Army representative on the scene, Colonel Wiliam F. Godson, agreed with the version of events presented by the Polish general staff.

[25] Neglecting the plight of the Jews,[25] Godson had only noted in his report the instances of Bolsheviks executing and mutilating civilians and Polish prisoners of war.

[25] The Nobel Prize-winning author Władysław Reymont, in an article published by Gazeta Warszawska, the main organ of the openly antisemitic National Democratic Party,[29] also denied that pogroms had taken place.

[28] The report was, however, highly critical of the activities of the Polish Army in Vilnius, noting that 65 Jews with no proven connections to the Bolsheviks had been killed, and that many arrests, robberies and abuses had occurred, while soldiers guilty of these acts had not been punished.

Lenin considered the city vital to his plans, and ordered its immediate recapture, with the Red Army attempting several counteroffensives in April 1919.

Polish forces in the area under general Stanisław Szeptycki numbered 11,000; Rydz-Śmigly had 8 infantry battalions, 18 cavalry squadrons and 18 guns in Vilnius itself.

[32] Representatives from the city were immediately sent to the Paris Peace Conference, and the Stefan Batory University in Vilnius, which had been closed in 1832 following the November 1830 Uprising, was reopened.

[32] Acting in accordance with his vision of a Polish-led "Międzymorze" federation of East-Central European states, Piłsudski on April 22, 1919, issued a bilingual statement, in Polish and Lithuanian, of his political intentions – the "Proclamation to the inhabitants of the former Grand Duchy of Lithuania", pledging to provide "elections [which will] take place on the basis of secret, universal and direct voting, without distinction between the sexes" and to "create an opportunity for settling your nationality problems and religious affairs in a manner that you yourself will determine, without any kind of force or pressure from Poland.

[34] The Lithuanian government in Kaunas, which viewed the city as the historic capital of the Grand Duchy of Lithuania, saw the Polish incursion as an occupation.

Relations between the Polish and Lithuanian governments, unable to reach a compromise over Vilnius, continued to worsen, destroying the prospects for Piłsudski's plan of the Międzymorze federation and leading to open hostilities in the ensuing Polish–Lithuanian War.