Kosovo was part of the Ottoman Empire from 1455 to 1912, at first as part of the "eyalet" of Rumelia, and from 1864 as a separate province ("vilayet"). During this time, Islam was introduced to the population. The Vilayet of Kosovo was an area much larger than today's Kosovo; it included all today's Kosovo territory, sections of the Sandžak region cutting into present-day Šumadija and Western Serbia and Montenegro along with the Kukës municipality, the surrounding region in present-day northern Albania and also parts of north-western North Macedonia with the city of Skopje (then Üsküp), as its capital. Between 1881 and 1912 (its final phase), it was internally expanded to include other regions of present-day North Macedonia, including larger urban settlements such as Štip ("İştip"), Kumanovo ("Kumanova") and Kratovo ("Kratova"). According to some historians, Serbs likely formed a majority of Kosovo from the 8th to the mid-19th century. Nevertheless, this claim is difficult to prove, as historians who base their works on Ottoman sources of the time give solid evidence that at least the western and central parts of Kosovo had an Albanian majority. The scholar Fredrick F. Anscombe shows that Prizren and Vučitrn ("Vulçitrin") had no Serbian population in early 17th century. Prizren was inhabited by a mix of Catholic and Muslim Albanians, while Vučitrn had a mix of Albanian and Turkish speakers, followed by tiny a Serbian minority. Gjakova was founded by Albanians in the 16th century, and Peja ("İpek") had a continuous presence of the Albanian Kelmendi tribe. Central Kosovo was mixed, but large parts of the Drenica Valley were ethnically Albanian. Central Kosovo, as well as the cities of Prizren, Gjakova, and the region of Has regularly supplied the Ottoman forces with levies and mercenaries.