Pope John VIII in the context of "Translation of the Bible"

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.

Charles the Fat (839 – 13 January 888) was the emperor of the Carolingian Empire from 881 to 887. A member of the Carolingian dynasty, Charles was the youngest son of Louis the German and Hemma, and a great-grandson of Charlemagne. He was the last Carolingian emperor of legitimate birth and the last to rule a united kingdom of the Franks.

Over his lifetime, Charles became ruler of the various kingdoms of Charlemagne's former empire. Granted lordship over Alamannia in 876, following the division of East Francia, he succeeded to the Italian throne upon the abdication of his older brother Carloman of Bavaria who had been incapacitated by a stroke. Crowned emperor in 881 by Pope John VIII, his succession to the territories of his brother Louis the Younger (Saxony and Bavaria) the following year reunited the kingdom of East Francia. Upon the death of his cousin Carloman II in 884, he inherited all of West Francia, thus reuniting the entire Carolingian Empire.

Branimir (Latin: Branimirus) was Duke of Croatia, reigning from 879 to c. 892. His country received papal recognition as a state from Pope John VIII on 7 June 879. During his reign, Duchy of Croatia retained its sovereignty from both Carolingian and Byzantine rule and became de jure independent. His rule marks the first real peak of early medieval Croatia. It was characterized by establishing closer relations with the Holy See, ecclestical re-organization in the former Roman province of Dalmatia, Christianization, and (re)construction of churches. Branimir is mentioned, for the period, in many reliable primary and secondary written and epigraphic sources.

Domagoj (Latin: Domagoi) was Duke of Croatia from 864 to 876, and the founder of the Domagojević dynasty. He usurped the Croatian throne after the death of Trpimir I and expelled his sons. He took a more active role in the Adriatic Sea than his predecessors, encouraged the use of force and waged many wars, specifically with the Arabs, Venice and the East Francia. Domagoj's belligerence and the tolerance and support of piracy caused bad relations with Pope John VIII, which was further worsened after Domagoj showed no mercy to his conspirators. Formally a Frankish vassal, he used to his advantage the Frankish succession crisis and started a successful revolt against Carloman of Bavaria. After his death in 876, Domagoj was succeeded by his son who was deposed and expelled by Zdeslav in 878.