He experienced a number of conflicts with the Bishop of Nantes and the Breton clergy. In 1240, he issued an edict expelling Jews from the duchy and cancelling all debts to them. He joined Louis IX of France in the Eighth Crusade in 1270, and survived the plague that killed the king. The duchy of Brittany experienced a century of peace, beginning with John I and ending with Duke John III's reign in 1341.