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Source: https://www.nationallibertyalliance.org/files/docs/foundingdocs/The%20Magna%20Carta%20.pdf

Abuses by King John caused a revolt by nobles who compelled him to execute this recognition of rights for both noblemen and ordinary Englishmen. It established the principle that no one, including the king or a lawmaker, is above the law.

What I notice is that the nobles didn't go outside of their own authority and this means that in reality they called themselves together. Most people will notice that King John was compelled to sign and such force in contract law invalidates the signature. Another truth about the facts at the time was that the crown was owned by the Pope and so in reality King john didn't have the authority to sign.

Two Pope's later both illegalities where solved and the Magna Carta became a rock solid contract as the Pope validated the Magna Carta when he agreed to it. Why he agreed to it isn't explained, but when you realize that at the time the crusades where in the beginning stages and anything that could hold up readiness would have to be dealt with. Well?

I encourage you to read the Magna Carta if you want to comprehend where common law comes from and want law on the land.