Battle of Warsaw (1920)
The battle of Warsaw was fought from August 12–25, 1920 as Red Army forces commanded by Mikhail Tukhachevsky approached the Polish capital of Warsaw and the nearby Modlin Fortress. On August 16, Polish forces commanded by Józef Piłsudski counterattacked from the south, disrupting the enemy's offensive, forcing the Russian forces into a disorganized withdrawal eastward and behind the Neman River. Estimated Russian losses were 10,000 killed, 500 missing, 30,000 wounded, and 66,000 taken prisoner, compared with Polish losses of some 4,500 killed, 10,000 missing, and 22,000 wounded.
Polish–Soviet War in 1920
The Polish military thrust soon met with the Red Army counterattack ("Soviet May Offensive"). The Soviet Southwest Front was commanded by Alexander Ilyich Yegorov. On 15 May the Soviet 15th Army attacked Polish positions near Ułła, and the 16th Army crossed the Berezina River between Borysów and Bobrujsk. Polish forces in that area, preparing for an offensive towards Żłobin, managed to push the Soviet forces back into the river, but were unable to pursue their own planned offensive. In the north Polish forces had done much worse. The Polish 1st Army was defeated and started a retreat towards Mołodeczno, pursued by the 15th army which had recaptured the territory between Dzwina and Berezyna. The Polish then attempted to take advantage of the exposed Soviet flanks, with Armia Rezerwowa attacking from Święciany and Grupa Skierskiego attacking from Borysów. Their plan was to envelop and crush the advancing Soviet forces, and have the 1st Army prevent any Soviet reinforcements. This time the 1st Army performed better, but the enveloping forces still failed to stop the Soviet advance. By the end of May, the front had stabilized near the small river of Auta, and Soviet forces begun preparing for their next attack, targeting the Połosck region. 
On May 24, 1920, the Polish–Ukrainian forces in the south clashed with the Semyon Budionny's famous 1st Cavalry Army ("Konarmia"). The Polish-Ukrainian forces succeeded in slowing and even defeating the Red Army on a number of occasions. Morale was high: the Polish-Ukrainian forces were eager to defend Ukraine and were confident in their ability to succeed. Polish High Command underestimated the quality of both Budionny's forces and the tactical role of cavalry, which hadn't fared well in the First World War trench warfare. Repeated attacks by Budionny's Cossack cavalry however, broke the Polish-Ukrainian front on June 5 and allowed mobile cavalry units to disrupt the Polish rear communication and logistics. By June 10, the Polish armies were in retreat along the entire front. Soviet forces under Golikow crossed Dniepr west of Czerniow cutting the rail communication in that region and Soviet forces under Yakir captured the Bila Tserkva. The Polish 3rd army in Kiev faced the danger of being completely enveloped.