The disastrous consequences of the erroneous and short-sighted, during the reigns of the first two Vasa kings, Cossack policies of the Polish Republic of Nobility were about to make their impact, first of many. In April and May 1648, in the Battle of Zhovti Vody and the Battle of Korsuń the joined Cossack-Tatar forces completely destroyed the Crown army, capturing Crown Hetmans Mikołaj Potocki and Marcin Kalinowski. Thousands of Registered Cossacks, sent into combat with the Polish forces, were persuaded by the rebels to change sides. As a result of the dramatic events, vast expanses of Dnieper Ukraine became engulfed in the spreading social upheaval and the region's separation from the Polish kingdom had begun.