In 1591, Fitzwilliam broke up the MacMahon lordship in Monaghan when The MacMahon, hereditary leader of the sept, resisted the imposition of an English sheriff; he was hanged and his lordship divided. There was an outcry, with several sources alleging corruption against Fitzwilliam, but the same policy was soon applied in Longford (territory of the O'Farrells) and East Breifne (Cavan — territory of the O'Reillys). Any attempt to further the same in the O'Neill and O'Donnell territories was bound to be resisted by force of arms.