Why was there a minority Muslim population living in the Balkan Peninsula by 1500 CE

The minority Muslim population living in the Balkan Peninsula by 1500 CE was due to the conquering of most of the peninsula by the Ottomans who also tried to get as many Turkic people that were Muslim in the new territories as to strengthen their positions. The Ottomans, once they managed to conquer the new territories in the Balkan, rushed to bring in as many Turkic people as possible there, and it was not just Ottoman Turks, but also Yuruks, Konyars, Cherkez and other Turkic people that were allies and were also Muslims. Also, they managed to convert some of the native populations very quickly, like part of the Arberi (later Albanians) which they used for support and also for spreading Islam.