John also fell foul of the Pope and the Catholic church, to the point whereby the Pope banned church services throughout England in 1207, before being excommunicated two years later.  This made him extremely unpopular within a God fearing country. In 1214, John tried unsuccessfully to recapture lost land in Northern France, and returned to England to raise yet more taxes from the Barons who refused to pay more, and rebelled against him. 
In doing so, the Barons took control of London, but were unable or unwilling to dispose of John completely, and the warring parties entered into dialog in early 1215, resulting in the fundamentals of the Magna Carta being discussed. 

In June of that year, John agreed to 63 clauses detailing rights and responsibilities of the Crown towards it's people.King John stayed at the Odiham Castle during the early part of June in 1215, as he rested here while traveling from Winchester to Runnymede, near Windsor, in order to sign the Magna Carta. 

The Magna Carta (Latin for 'Great Charter'), was an agreement between the King and the land Barons.

King John's castle, nr. Odiham