Although initially stout opponents of the advancing Turks, Albanian chiefs ultimately came to accept the Ottomans as sovereigns. The resulting alliance facilitated the mass conversion of Albanians to Islam. Given that the Ottoman Empire's subjects were divided along religious (rather than ethnic) lines, Islamisation greatly elevated the status of Albanian chiefs. Prior to this, they were organised along simple tribal lines, living in the mountainous areas of modern Albania (from Kruje to the Šar range). Soon, they expanded into a depopulated Kosovo, as well as northwestern Macedonia, although some might have been autochthonous to the region. However, Banac favours the idea that the main settlers of the time were Vlachs. Centuries earlier, Albanians of Kosovo were predominantly Christian and Albanians and Serbs for the most part co-existed peacefully. The Ottomans appeared to have a more deliberate approach to converting the Roman Catholic population of whom were mostly Albanians as compared to adherents of Eastern Orthodoxy who were mostly Serbs, as they viewed the former less favorably due to its allegiance to Rome, a competing regional power.