Just to nit pick this one. The Balkans were soundly in the hands of the Byzantines. There had been incursions by Islamic raiders, but nothing near occupation of the Balkans. Anatolia doesn’t even fall until the Battle of Manzikert. Which was a loss to the Seljuk Turks. In short, control of the Balkans goes like this,
Byzantine, Slavic powers(Serbs, Albanians, Huns, Greeks…), Crusaders(the fourth crusade sacked Byzantium stabbing Orthodox Christians in the back), Ottomans, Austrians and then back to Slavic Nations. Many an Islamic Army knocked on the gates of Constantinople, but it was the Ottomans, aided by their Italian engineers, who seized the city and all the Balkans as well, and the Ottomans were never ones to tolerate rivals be they Muslims or Christians.
