The Battle of Warsaw was fought in July 1656 between a Swedish-Brandenburger army led by King Charles X Gustav of Sweden and Elector Friedrich Wilhelm of Brandenburg and a Polish-Tatar army led by King Jan II Casimir. Poland-Lithuania's defeat resulted in Warsaw's fall to the Swedish invaders.
On 29 June 1656, King Charles Gustav allied with the Elector of Brandenburg-Prussia, promising him sovereignty in four Polish voivodeships in exchange for his help against the Poles. On 28 July, the combined Swedish-Brandenburger army advanced on Warsaw; their army consisted of 12,500 cavalry and 5,500 infantry. King Jan II Casimir and his army of 35,500 cavalry and 4,500 infantry (38,000 Polish-Lithuanian troops and 2,000 Crimean Tatars) crossed the Vistula and met the invaders north of Warsaw's suburb of Praga.
On the first day of battle, the Poles dug in and repelled Charles Gustav's attack on the right bank of the Vistula. On the second day, Charles attacked through the Bialoleka Forest before the Polish hussars could react. 800 Polish hussars charged the three lines of reiters guarding Charles' flanks, breaking through two regiments before being stopped by flank fire. Charles was wounded during the fighting, but the Swedes and Germans held their ground, forcing Jan Casimir to withdraw across the Vistula bridge. On the third day, the Polish-Lithuanian cavalry escaped across the Vistula and Jan Casimir abandoned Warsaw for a second time. His army retreated unbroken and with relatively few losses, regrouping at Lublin. Meanwhile, the Brandenburgers would halt their advance in Greater Poland and refuse to advance any further, forcing Charles to abandon Warsaw and withdraw north to Royal Prussia rather than face the much larger Polish army alone.