 Particularly resented was the attempt to impose Roman Catholicism on the unwilling Ukrainians, who had been traditionally Eastern Orthodox.About ten thousand rebels proceeded from the Zaporizhian Sich towards the upper Dnieper territories, overrunning the Polish forces stationed there.The rebels captured and executed the Hetman of the registered Cossacks Hryhoriy Chorny for his pro-Polish stance and support of the Union of Brest, and subsequently came to an agreement on a new leadership by nominating Fedorovych for the position of Hetman.