Why did the Magna Carta fail to prevent civil war in 1215?

The Magna Carta failed to prevent civil war in 1215 because it was essentially a stage in ineffective negotiations rather than a lasting peace settlement. While the charter was intended to provide guarantees against the arbitrary rule of King John, it was quickly rendered unworkable by the intransigence of certain barons and the king’s immediate appeal to Pope Innocent III.12

The Pope, who had previously accepted England as a papal fief, took the king’s side and declared the charter null and void, arguing that it violated his rights as a feudal lord. This papal intervention effectively undermined the document's authority, leaving the conflict unresolved. Consequently, the agreement failed to bridge the deep-seated distrust between the crown and the rebels, leading to a continuation of hostilities that persisted until after John’s death in 1216.132