Heraclius I in the context of "Phocas"

The Duchy of Croatia (Modern Croatian: Kneževina Hrvatska; also Duchy of the Croats, Modern Croatian: Kneževina Hrvata; Latin: Ducatus Chroatorum; Greek: Χρωβατία) was a medieval state that was established by White Croats who migrated into the area of the former Roman province of Dalmatia c. 7th century AD. Throughout its existence the Duchy had several seats – namely, Klis, Solin, Knin, Bijaći and Nin. It comprised the littoral – the coastal part of today's Croatia – except Istria, and included a large part of the mountainous hinterland as well.

The Croats settled in Dalmatia after defeating the Pannonian Avars, during the time of Byzantine emperor Heraclius I. The Duchy was in the center of competition between the Byzantine Empire and the Carolingian Empire for rule over the area. Croatian rivalry with Venice emerged in the first decades of the 9th century and would continue through the following centuries. Croatia also waged battles with the Bulgarian Empire (founded c. 681; Bulgar-Croatian relations improved greatly afterwards) and with the Arabs; it also sought to extend its control over important coastal city-states under the rule of Byzantium. Croatia experienced periods of vassalage to the Franks or to the Byzantines and of de facto independence until 879, when Duke Branimir was recognized as an independent ruler by Pope John VIII. The Duchy was ruled by the Trpimirović and Domagojević dynasties from 845 to 1091. Around 925, during the rule of Tomislav, Croatia became a kingdom.