Magna Carta

Magna Carta, a pivotal moment in the emergence of constitutional government, institutionalised constraints on royal power. We depict it as an optimal agreement between two coalitions capable of violence: the king's loyal coalition of barons and the rebel barons. This type of agreement is more likely to emerge when the king extracts large rents, when the distribution of rents among barons is egalitarian, and when barons can move large resources away from the king. Under these conditions, even the baron that already enjoys the largest rents would be willing to lead a rebellion, and rebels have large resources that they can use to defeat the loyalists. We test the predictions of our model with a newly collected data on the universe of barons and their lands in England in 1215