What led to the creation of magna carta, known as the cornerstone of modern english law?

The missteps of king John and increased opposition from the barons

It was first drafted by the Archbishop of Canterbury to make peace between the unpopular King and a group of rebel barons. It promised the protection of church rights, protection for the barons from illegal imprisonment, access to swift justice, and limitations on feudal payments to the Crown, to be implemented through a council of 25 barons.