The Principality of Salerno was a medieval Southern Italian state, formed in 851 out of the Principality of Benevento after a decade-long civil war. It was centred on the port city of Salerno. Although it owed allegiance at its foundation to the Carolingian emperor, it was de facto independent throughout its history and alternated its allegiance between the Carolingians and their successors in the West and the Byzantine emperors in the east.