In 855 Boris I of Bulgaria attacked Dalmatian Croatia trying to expand his state to the Adriatic, but was defeated probably in Eastern Bosnia and signed a peace treaty with Trpimir.
Aastal 855 ründas Bulgaaria Boris I Dalmaatsia Horvaatiat, püüdes laiendada oma riiki Aadria mereni, kuid sai arvatavasti Ida-Bosnias kaotuse ja sõlmis Trpimiriga rahulepingu.