from www.cia.gov
The Ottoman Turks first focused their conversion campaigns on the Roman Catholic Albanians of the north and then on the Orthodox population of the south. For example, the authorities increased taxes, especially poll taxes, to make conversion economically attractive. During and after a Christian counteroffensive against the Ottoman Empire from 1687 to 1690, when Albanian Catholics revolted against their Muslim overlords, the Ottoman pasha of Pec, a town in the south of present-day Yugoslavia, retaliated by forcing entire Albanian villages to accept Islam. Albanian beys then moved from the northern mountains to the fertile lands of Kosovo, which had been abandoned by thousands of Orthodox Serbs fearing reprisals for their collaboration with the Christian forces.
Most of the conversion's to Islam took place in the lowlands of the Shkumbin River valley, where the Ottoman Turks could easily apply pressure because of the area's accessibility. Many Albanians, however, converted in name only and secretly continued to practice Christianity. Often one branch of a family became Muslim while another remained Christian, and many times these families celebrated their respective religious holidays together