Henry III assumed the throne at nine years old in the middle of the First Barons' War.
Henry III of England . The son of King John and Isabella of Angoulême , Henry assumed the throne when he was only nine in the middle of the First Barons ' War . Magna Carta Libertatum ( Medieval Latin for `` the Great Charter of the Liberties '' ) , commonly called Magna Carta ( also Magna Charta ; '' ( the ) Great Charter '' ) , is a charter agreed to by King John of England at Runnymede , near Windsor , on 15 June 1215 .