Simeon I sent a small army led by Thedore Sigritsa and Marmais but they were ambushed and killed. Zaharija sent their heads and armour to Constantinople. This action provoked a major retaliatory campaign in 924. A large Bulgarian force was dispatched, accompanied by a new candidate, Časlav, who was born in Preslav to a Bulgarian mother. The Bulgarians ravaged the countryside and forced Zaharija to flee to the Kingdom of Croatia.

This time, however, the Bulgarians had decided to change the approach towards the Serbs. They summoned all Serbian župans to pay homage to Časlav, had them arrested and taken to Preslav. Serbia was annexed as a Bulgarian province, expanding the country's border to Croatia, which at the time had reached its apogee and proved to be a dangerous neighbour. The annexation was seen by the Bulgarians as a necessary move since the Serbs had proved to be unreliable allies and Simeon I had grown wary of the inevitable pattern of war, bribery and defection. According to Constantine VII's book De Administrando Imperio Simeon I resettled the whole population to the interior of Bulgaria and those who avoided captivity fled to Croatia, leaving the country deserted.