Article: In the aftermath of John's death William Marshal was declared the protector of the nine-year-old Henry III. The civil war continued until royalist victories at the battles of Lincoln and Dover in 1217. Louis gave up his claim to the English throne and signed the Treaty of Lambeth. The failed Magna Carta agreement was resuscitated by Marshal's administration and reissued in an edited form in 1217 as a basis for future government. Henry III continued his attempts to reclaim Normandy and Anjou until 1259, but John's continental losses and the consequent growth of Capetian power in the 13th century proved to mark a "turning point in European history".

Question: What agreement failed?
Magna Carta