The battle of Chocim (or Khotin) was a Polish-Lithuanian victory during the Polish-Ottoman War of 1620-1621. The Ottoman victory at Cecora in 1620 had encouraged Sultan Osman II to lead a massive army north on an invasion of the Ukraine (then part of the Commonwealth of Poland-Lithuania). The size of his army in not entirely clear, but it contained at least 100,000 men and may have been as large as 250,000.
The Commonwealth responded to the defeat at Cecora and the threat of invasion by raising a much larger army than in 1620. The Polish-Lithuanian contingent was 30,000 strong, supported by as many Cossacks. The Commonwealth army took up a defensive stance at Chocim, building a sophisticated series of fortifications that allowed them to use their cavalry to launch counterattacks during the battle. The Commonwealth camp covered some eight square kilometres.
The Ottoman army arrived at Chocim on 2 September and launched a series of attacks on the Polish camp. These failed to break into the defended area. Osman also attempted to isolate the camp by blocking their access to the nearby Dniester River. However, his own large army was just as vulnerable to supply problems, and by the end of September both armies were running short of food and ammunition. After the failure of a final assault on 28 September, Osman II entered into peace negotiations. These restored the pre-war situation, confirming the border between the Commonwealth and the Ottoman Empire (and leaving Moldavia under Ottoman control).
Osman’s invasion having failed, he then looked for a scapegoat and settled on the Janissaries. His attempts to reform them ended in a Janissary revolt that saw Osman overthrown and replaced, first by his uncle Mustafa and then by Murad IV. Meanwhile the absence of most of the Commonwealth’s army in the south encouraged Gustav Adolf of Sweden to invade Estonia, renewing the Polish-Swedish War of 1600-1629.