William of Villehardouin in the context of "Lordship of Argos and Nauplia"

Charles I (Italian: Carlo; early 1226/1227 – 7 January 1285), commonly called Charles of Anjou or Charles d'Anjou, was King of Sicily from 1266 to 1285. He was a member of the Capetian dynasty and the founder of the House of Anjou-Sicily. Between 1246 and 1285, he was Count of Provence and Forcalquier in the Holy Roman Empire and Count of Anjou and Maine in France. In 1272 he was proclaimed King of Albania, in 1277 he purchased a claim to the Kingdom of Jerusalem, and in 1278 he became Prince of Achaea after the previous ruler, William of Villehardouin, died without heirs.

The youngest son of Louis VIII of France and Blanche of Castile, Charles was destined for a church career until the early 1240s. He acquired Provence and Forcalquier through his marriage to Beatrice. His attempts to restore central authority brought him into conflict with his mother-in-law, Beatrice of Savoy, and the nobility. He relinquished control of Forcalquier to his mother-in-law in 1248, although she returned it to him in 1256. Charles received Anjou and Maine from his brother, Louis IX of France, in appanage. He accompanied Louis during the Seventh Crusade to Egypt. Shortly after he returned to Provence in 1250, Charles forced three wealthy autonomous cities—Marseille, Arles and Avignon—to acknowledge his suzerainty.

The Battle of Pelagonia or Battle of Kastoria took place in early summer or autumn 1259, between the Empire of Nicaea and an anti-Nicaean alliance comprising Despotate of Epirus, Kingdom of Sicily and the Principality of Achaea. It was a decisive event in the history of the Eastern Mediterranean, ensuring the eventual reconquest of Constantinople and the end of the Latin Empire in 1261.

The rising power of Nicaea in the southern Balkans, and the ambitions of its ruler, Michael VIII Palaiologos, to recover Constantinople, led the formation of a coalition between the Epirote Greeks, under Michael II Komnenos Doukas, and the chief Latin rulers of the time, the Prince of Achaea, William of Villehardouin, and Manfred of Sicily. The details of the battle, including its precise date and location, are disputed as the primary sources give contradictory information; modern scholars usually place it either in July or in September, somewhere in the plain of Pelagonia or near Kastoria. It appears that the barely concealed rivalries between the Epirote Greeks and their Latin allies came to the fore in the lead-up to the battle, possibly fanned by Palaiologos' agents. As a result, the Epirotes abandoned the Latins on the eve of the battle, while Michael II's bastard son John Doukas defected to the Nicaean camp. The Latins were then set upon by the Nicaeans and routed, while many nobles, including Villehardouin, were taken captive.

The War of the Euboeote Succession was fought in 1256–1258 between the Prince of Achaea, William of Villehardouin, and a broad coalition of other rulers from throughout Frankish Greece who felt threatened by William's aspirations. The war was sparked by Villehardouin's intervention in a succession dispute over the northern third of the island of Euboea, which was resisted by the local Lombard barons (the "triarchs") with the aid of the Republic of Venice. The Lord of Athens and Thebes, Guy I de la Roche, also entered the war against William, along with other barons of Central Greece. Their defeat at the Battle of Karydi in May/June 1258 effectively brought the war to an end in an Achaean victory, although a definite peace treaty was not concluded until 1262.