Henry III assumed the throne 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 . In 1263 one of the more radical barons , Simon de Montfort , seized power , resulting in the Second 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 . Neither side stood behind their commitments , and the charter was annulled by Pope Innocent III , leading to the First Barons ' War . The Treaty of Lambeth of 1217 , also known as the Treaty of Kingston to distinguish it from the Treaty of Lambeth of 1212 , was a peace treaty signed by Prince Louis of France in September 1217 ending the campaign known as the First Barons ' War to uphold the claim by Louis to the throne of England .