Bulgarian–Serbian wars of 917–924
Soon after Simeon I (r. 893–927) ascended to the throne, he successfully defended Bulgaria's commercial interests, acquired territory between the Black Sea and the Strandzha mountains, and imposed an annual tribute on the Byzantine Empire as a result of the Byzantine–Bulgarian war of 894–896.
[3][4] The outcome of the war confirmed the Bulgarian domination on the Balkans but also exposed the country's vulnerability to foreign intervention under the influence of the Byzantine diplomacy.
[7][8] Unlike his predecessors, Simeon I's ultimate ambition was to assume the throne of Constantinople as a Roman emperor, creating a joint Bulgarian–Roman state.
[12][13][14] However, after a coup d'état in February 914 the new Byzantine government under Constantine VII's mother Zoe Karbonopsina revoked the concessions and the hostilities continued.
As part of their efforts the strategos of Dyrrachium Leo Rhabdouchos was instructed to negotiate with the Serbian prince Petar Gojniković, who was a Bulgarian vassal.
Petar Gojniković responded positively but the Bulgarian court in Preslav was warned about the negotiations by prince Michael of Zahumlje, a loyal ally of Bulgaria, and Simeon I was able to prevent an immediate Serb attack.
[17][19][20] Following the victories in 917, the way to Constantinople lay open, but Simeon I decided to deal with prince Petar Gojniković before advancing further against the Byzantines.
[26][27] 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.
[28] The annexation was seen by the Bulgarians as a necessary move since the Serbs had proved to be unreliable allies[28] and Simeon I had grown wary of the inevitable pattern of war, bribery and defection.
[29] 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.
Similarly to the case of Serbia, Croatia was invaded in the context of the Byzantine–Bulgarian conflict, because king Tomislav (r. 910–928) was a Byzantine ally and harboured enemies of Bulgaria.
