 John's chronicle is a key primary source for the history of Slavic peoples and polities in Dalmatia during the 9th and 10th centuries, for which he probably drew on earlier documents.He distinguishes between the Narentines, who lived about the mouth of the Neretva River, and another, more northerly group that would give rise to the principality of Croatia and later still, the kingdom of Croatia.John reports on the troublesome dealings of Doge John (829–836) and his successor Peter (836–864) with the Neretva Slavs; the "Pactum Lotharii" of 840 and the Venetian-Frankish alliance against Slavic piracy; Domagoj and the wars about the Istrian region; the coup of the Slavic principality by Zdeslav; the usurper Branimir; and naval warfare against the Narentine Slavs in 887 and 948.