According to Porphyrogenitus, the Bulgars wanted to continue their conquest of the Slavic lands and to force the Serbs into subjugation. Khan Presian (r. 836–852) launched an invasion into Serbian territory in 839, which led to a war that lasted for three years, in which the Serbs were victorious. The Bulgarian army was heavily defeated and lost many men. Presian made no territorial gains and was driven out by the army of Vlastimir. The Serbs held out in their hardly accessible forests and gorges, and knew how to fight in the hills. The war ended with the death of Theophilos in 842, which released Vlastimir from his obligations to the Byzantine Empire.

The defeat of the Bulgars, who had become one of the greater powers in the 9th century showed that Serbia was an organized state, fully capable of defending its borders; a very high military and administrative organizational frame to present such effective resistance.