sentences:  The Croatian Prince Mislav (835–845) built up a formidable navy, and in 839 signed a peace treaty with Pietro Tradonico, doge of Venice.The Venetians soon proceeded to battle with the independent Slavic pirates of the Pagania region, but failed to defeat them.The Bulgarian king Boris I (called by the Byzantine Empire Archont of Bulgaria after he made Christianity the official religion of Bulgaria) also waged a lengthy war against the Dalmatian Croats, trying to expand his state to the Adriatic.