In the 9th century the Bulgarians became masters of Naissus, but had to cede it to the Hungarians in the iith century, from whom the Byzantine emperor Manuel I.
the Bulgarians conquered the southern portion of the country and Epirus as far as Khimara; under their powerful tsar Simeon (893-927), who defeated the Servians, they established their rule on the Adriatic littoral, except at Durazzo, which remained Byzantine, and colonized these regions in great numbers.
When Bulgaria under the Berlin Treaty was constituted an autonomous principality under the suzerainty of Turkey, the tsar recommended his nephew to the Bulgarians as a candidate for the newly created throne, and Prince Alexander was elected prince of Bulgaria by unanimous vote of the Grand Sobranye (April 29, 1879).
A serious breach with Russia followed, which was widened by the part which the prince subsequently played in encouraging the national aspirations of the Bulgarians.
The terror of their name had long preceded them, and Bela, in 1235 or 1236, sent the Dominican monk Julian, by way of Constantinople, to Russia, to collect information about them from the "ancient Magyars" settled there, possibly the Volgan Bulgarians.