You may remember that the country was being ruled by King John. Needless to say John had been involved in
fighting in France, parts of which he still ruled. In order to pay for the fighting
he had to increase the taxes he charged his English barons who in turn increased the taxes they took from their peasants.
Unfortunately John wasn’t very good at this battle winning game and by 1214 he had lost Normandy, Anjou and Brittany. He had to come back and tell this
to some of the nobles in England who thought they still had land in France but now didn’t. This was on top of the fact that he had taxed them to pay for this loss.
If you think about it, the same sort of thing still goes on. Most adults in our time pay their taxes. If you work then it is taken from your salary or
your wages. All the money goes to the government and they decide what to do with it. Hopefully they don't spend much of it on fighting and losing battles but the
taxes do pay for the armed forces. The government will also pay to have advisers to, hahaha, give them advice. In the old times the king would have advisers too.
But the barons were becoming unhappy and, next year, they became even more unhappy.
John had also lost another battle, without any fighting, when the Pope cut him off from the Catholic Church because John had tried to overrule the
monks in Canterbury when a new Archbishop of Canterbury had to be chosen. Luckily he was re-instated a little bit later.