In this passage from the 2005 book by Dietmar Müller we can read an interesting passage about how the Serbian and Montenegrin invaders violently converted 12,000 Albanians to the Slavic faith, as well as killing 800 Albanians who refused. The Slavic invaders stopped with the atrocities only when Austro-Hungary forced them.

“Montenegrin integration policy was distinguished by one measure that was apparently not pursued by the Serbs: the forced baptism of Albanian and Slavic Muslims in the towns of Plav, Gusinje, Peja, and Gjakova. In an operation coordinated between several ministries, of which King Nikola Petrović Njegoš was apparently also aware, 12,000 Muslims were forcibly Christianized in the first two towns alone by February 1913, and 800 people who refused to undergo this procedure were killed.

Only when Catholic Albanians from Pejë and Gjakova were also included did the forced baptisms have to be stopped under pressure from Austria-Hungary. The Muslims, who before 1912 made up about three-quarters of the total population of this area, therefore filled the ranks of the Kaçak movement and fled in considerable numbers to Scutari and Albania.”

Source

Staatsbürger aus Widerruf Juden und Muslime als Alteritätspartner im rumänischen und serbischen Nationscode : ethnonationale Staatsbürgerschaftskonzepte 1878-1941 by Dietmar Müller, 2005. Kosovo and the Albanians in the Serbian Nation Code, 1880-1914