The long-lasting Cossack uprising began in 1648 and was led by Bohdan Khmelnytsky. It was a great national and social movement, as the increasingly exploited Rus' peasant masses joined the Cossacks to fight their "szlachta" oppressors. Polonization, catholicizing, state support for the Uniate Church (especially in western Ukraine) at the expense of the often persecuted Orthodox religion, and denying the Ukrainian people cultural opportunities were some of the factors that contributed greatly to the unrest. In spite of the suppression, during the first half of the 17th century the Rus' elements in the region matured, consolidated and gained strength at all levels of society. Accordingly, a great majority of the Ukrainian nobility from the Kiev and Bratslav Voivodeships and the Ukrainian urban people joined the uprising as well.