In 1689-90 a Habsburg army advanced deep into Ottoman Rumelia with Serb and Albanian support; when it was thrown back, Ottoman and Tatar forces conducted reprisals and Patriarch Arsenije III Carnojevic led a large body of Serbs north across the Danube and Sava under privileges granted by Emperor Leopold I in 1690-1691, which recognised the patriarch as head of the Serbian Orthodox Church in the Monarchy and granted the migrants ecclesiastical and communal autonomy until their abolition in 1912. A second movement followed the failed Habsburg campaign of 1737-39 under Patriarch Arsenije IV. The migrants of 1690 settled in southern Hungary, including Szentendre and Buda, and in Srem, Banat and along the military frontier, where they formed the demographic basis of later Vojvodina and of the Serbian Orthodox metropolitanate of Karlovci. The size of the 1690 movement is disputed, with sources giving 30,000-40,000 people or 37,000 families; the demographic effect on Kosovo and Old Serbia, and whether it opened the way for Albanian settlement there, is one of the most politically contested questions in Balkan historiography, argued differently by Serbian and Albanian historians.
Serb populations fled Ottoman reprisals after failed Habsburg offensives, moving north under their patriarchs into Habsburg Hungary
No usable denominator exists and the question is politically contested. Ottoman tax registers for the sanjaks of Old Serbia and Kosovo record households rather than a comparable population total, and the size of the Orthodox Serb population there around 1690 is disputed between Serbian and Albanian historiography. Even the migration figure is unsettled: Patriarch Arsenije III's own account speaks of some 30,000 souls, later Habsburg and Serbian sources of 37,000 families or up to 80,000 people.
No death toll can be established. Contemporary accounts describe Ottoman and Tatar reprisal killings in 1690 and heavy mortality from hunger and disease among the migrants during the winter crossing, but no figures were recorded.
Kosovo, Serbia, Hungary