Why was King John forced to sigh the Mangna Carta?

Answer 1

He was forced to sign the Magna Carta because of all the people supporting it. Without people a King couldn't be a King right? So he was forced to sign it. Signing it limited his power which was also the reason why the Magna Carta was created - since the king - King John - had been unjust and unfair. The Roman church at the time was in some cases more important than the King. Since God was more in the focus, and the church highly approved of the Magna Carta, and the church was supported by the people King John didn't have much of a chance of NOT signing the document.

Answer 2

Rogue nobles resisted his reign, even though he tried to gain support from the Church and did receive protection under his announcement of his intent to become a crusader. The nobles still didn't care, and marched on London and Exeter, and John finally faced them at Runnymede on 15 June, 1215. John essentially was forced to sign the Magna Carta, because if he didn't, the nobles would continue to ravage the country.