On 22 March 1642 the Catholic hierarchy held a synod at Kells and almost unanimously agreed that the rebellion was a just war. They drafted a Confederate Oath of Association in May and Meath lawyer Nicholas Plunkett encouraged Catholic nobles to take up the oath. After the outbreak of the English Civil War, an assembly was held in Kilkenny and the provisional government of Confederate Ireland was established, which took up arms with the Royalists against the Parliamentarians. The Royalists were crushed by Oliver Cromwell, who then set about ending the Irish Confederate Wars by engaging in an unquestionably brutal conquest of Ireland, resulting in the death of up to 40% of the island's population.