In 1262, Henry obtained a Papal Bull negating the Provisions; war broke out in 1263 as de Montfort aimed to enforce them. Edward vacillated in his loyalties but eventually settled as a royalist along with Henry’s brother, Richard, who returned from an elected kingship in Germany. In 1264, they suffered a disastrous defeat at Lewes. All three were imprisoned, but Henry was still technically king. De Montfort controlled the English government.

Discontent grew with de Montfort’s leadership, which featured the partisan autocracy he had rejected. In 1265, Edward escaped captivity and formed a coalition that included old allies of de Montfort and promised fair government. In their decisive victory at Evesham, de Montfort, and his leading men were all slain.

Edward was known as the leopard due to his reputation as fierce but changeable. Following Evesham, Henry prioritized revenge, disinheriting defeated parties; revolt continued throughout the land with Kenilworth as the remaining stronghold. Edward led military operations, periodically seeking non-violent terms instead. Advisers like Richard and the papal legate helped negotiate the Dictum of Kenilworth in 1266 and the realm shifted towards conciliation. The Statute of Marlborough (1268) furthered technical statutory reform.