In the article the author analyses the written sources on the participation of the Slavic population, the so-called “Σχλαβηνίας” or “Sklaviniis”, in the wars of the First Bulgarian State in the early 9th century. During the reign of the khans Krum and Omurtag there was political eminence of the First Bulgarian State. One of the determining factors of this process was the conquest of new territories where the tribes of the Slavs or “Σχλαβηνίας” lived. Being the most numerous ethnic group of the First Bulgarian State they maintained close ties both with other nations and with each other, which led to mutual influences in material and military cultures. The confirmation of this can be the participation of “Σχλαβηνίας” in many military conflicts throughout the 9th century.