"protector of the Christian people" on its head by agreeing to pay the Khan of Crimea with jasyr or Christian captives. Initially these were Polish prisoners, but later whole tracts of land in Ukraine were assigned for Tatars to capture anyone (including Jews who moved en masse into the palatinates of Ukraine after 1569) and lead them to be sold on the slave markets of Kaffa. Beginning On January 25, 1648, Khmelnytsky brought a contingent of 400–500 Cossacks to the Zaporizhian Sich and quickly killed the guards assigned by the Commonwealth to protect the entrance. Once at the Sich, his oratory and diplomatic skills struck a nerve with oppressed Ruthenians. As his men repelled an attempt by Commonwealth forces to retake the Sich, more recruits joined his cause. The Cossack Rada elected him Hetman by the end of the month. Khmelnytsky threw most of his resources into recruiting more fighters. He sent emissaries to Crimea, enjoining the Tatars to join him in a potential assault against their shared enemy, the Commonwealth. By April 1648 word of an uprising had spread throughout the Commonwealth. Either because they underestimated the size of the uprising, or because they wanted to act quickly to prevent it from spreading, the Commonwealth's Grand Crown Hetman Mikołaj Potocki and Field Crown Hetman Marcin Kalinowski sent 3,000 soldiers under the command of Potocki's son, Stefan, towards Khmelnytsky, without waiting to gather additional forces from Prince Jeremi Wiśniowiecki. Khmelnytsky marshalled his forces and met his enemy at the Battle of Zhovti Vody, which saw a considerable amount of defections on the field of battle by Registered Cossacks, who changed their allegiance from the Commonwealth to Khmelnytsky. The victory was quickly followed by rout of the Commonwealth's armies at the Battle of Korsuń, which saw both the elder Potocki and Kalinowski captured and imprisoned by the Tatars. In addition to the loss of significant forces and military leadership, the Polish state also lost King Władysław IV Vasa, who died in 1648, leaving the Crown of Poland leaderless and in disarray at a time of rebellion. The szlachta was on the run from its peasants, their palaces and estates in flames. All the while, Khmelnytsky's army marched westward. Khmelnytsky stopped his forces at Bila Tserkva and issued a list of demands to the Polish Crown, including raising the number of Registered Cossacks, returning churches taken from the Orthodox faithful and paying