PL
Ukraine was incorporated to the Crown (the Kingdom of Poland) under the Act of Union of Lublin, establishing the Commonwealth of Two Nations. The article presents the most important causes of the process of Ukraine’s gradual separation from the Commonwealth. It points out the role of Cossacks and also deals with the religious issues in the 17th century. It shows the causes of the Cossack Uprisings including the most significant one from 1648, as well as the politics of its leader, Bohdan Chmielnicki, who used to oscillate between Poland and Moscow.