structural:expansion
Kiev offensive

On 17 April 1920, the Polish General Staff ordered the armed forces to assume attack positions. The Red Army, which had been regrouping since 10 March, was not fully ready for combat. The main goal of the military operation was to create a Ukrainian state, formally independent but under Polish patronage, which would separate Poland from Russia.

On 25 April, the southern group of Polish armies under Piłsudski's command commenced an offensive in the direction of Kiev. The Polish forces were assisted by thousands of Ukrainian soldiers under Petliura, who represented the Ukrainian People's Republic.

Alexander Yegorov, commander of the Russian Southwestern Front, had at his disposal the 12th and 14th Armies. They faced the invading force, but were small (15,000 battle-ready soldiers), weak, poorly equipped and had been distracted by peasant rebellions in Russia. Yegorov's armies had been gradually reinforced since the Soviets had found out of the Polish war preparations.

On 26 April, in his "Call to the People of Ukraine", Piłsudski told his intended audience that "the Polish Army would only stay as long as necessary until a legal Ukrainian government took control over its own territory". However, although many Ukrainians were anti-communist, many were anti-Polish and resented the Polish advance.

The well-equipped and highly mobile Polish 3rd Army under Rydz-Śmigły quickly overpowered the Red Army in Ukraine. The Soviet 12th and 14th Armies had for the most part declined to engage in combat and suffered limited losses; they withdrew or were pushed past the Dnieper River. On 7 May, the combined Polish–Ukrainian forces, led by Rydz-Śmigły, encountered only token resistance as they entered Kiev, mostly abandoned by the Soviet military.

The Soviets proceeded with their first counteroffensive using the Western Front forces. Following the order of Trotsky, Mikhail Tukhachevsky launched an offensive on the Belarusian front before the (planned by the Polish command) arrival of Polish troops from the Ukrainian front. On 14 May, his forces attacked the somewhat weaker Polish armies there and penetrated the Polish-held areas (territories between the Daugava and the Berezina Rivers) to the depth of 100 km. After two Polish divisions arrived from Ukraine and the new Reserve Army was assembled, Stanisław Szeptycki, Kazimierz Sosnkowski and Leonard Skierski led a Polish counteroffensive from 28 May. The result was the Polish recovery of the bulk of the lost territory. From 8 June, the front had stabilised near the Avuta River and remained inactive until July.

This Polish thrust into Ukraine was met with Red Army counterattacks from 29 May. By that time, Yegorov's Southwestern Front had been considerably reinforced and he initiated an assault maneuver in the Kiev area.

Semyon Budyonny's 1st Cavalry Army (Konarmia) conducted repeated attacks and broke the Polish–Ukrainian front on 5 June. The Soviets deployed mobile cavalry units to disrupt the Polish rearguard and target communications and logistics. By 10 June, the Polish armies were in retreat along the entire front. Following Piłsudski's order, Rydz-Śmigły, with the Polish and Ukrainian troops under his command, abandoned Kiev (the city was not being attacked) to the Red Army.