Mortimer was created Earl of March in the parliament held in October, 1328, at Salisbury, where John of Eltham was made Earl of Cornwall and James, Butler of Ireland, Earl of Ormonde.  His assumption of this new title at last roused the sluggish indignation of Earl Henry of Lancaster, who felt that his own marcher interests were compromised, and bitterly resented the vain use made of his name, while he was carefully kept without any control of policy.  He refused to attend the Salisbury parliament, though he and his partisans mustered in arms in the neighbourhood of that city.  Civil war seemed imminent, and Mortimer’s Welshmen devastated Lancaster’s earldom of Leicester, but Archbishop Meopham (who had lately succeeded Reynolds in the primacy) managed to patch up peace.  Not long afterwards Lancaster was smitten with blindness, and was thenceforth unable to take an active part in public affairs.  Mortimer again triumphed for the moment, and, with cruel malice, excepted Lancaster’s confidential agents from the pardon which he was forced to extend to the earl.  His success over Lancaster was materially facilitated by the weakness of Edmund, Earl of Kent, who, after joining with Earl Henry in his refusal to attend the Salisbury parliament, deserted him at the moment of the capture of Leicester by the Earl of March.  But his treachery did not save him from Mortimer’s revenge.  In conjunction with the queen, Mortimer plotted to lure on Earl Edmund to ruin.  Their agents persuaded him that Edward II. was still alive and imprisoned in Corfe castle, and urged him to restore his brother to liberty.  The earl rose to the bait, and agreed to be party to an insurrection which was to restore Edward of Carnarvon to freedom, if not to his throne.  When Kent was involved in the meshes, he was suddenly arrested in the Winchester parliament of March, 1330, and accused of treason.  Convicted by his own speeches and letters, he was adjudged to death by the lords, and on March 19 beheaded outside the walls of the city.

The fall of Kent convinced Lancaster that his fate would not be long delayed, and that his best chance of saving himself and his cause lay in stirring up the king to energetic action against the Earl of March.  The death of his uncle irritated Edward, who at seventeen was old enough to feel the degrading nature of his thraldom, and was eager to govern the kingdom of which he was the nominal head.  In June, 1330, the birth of a son, the future Black Prince, to Edward and Philippa seems to have impressed on the young monarch that he had come to man’s estate.  Lancaster accordingly found him eager to shake off the yoke of his mother’s paramour.  The opportunity came in October, 1330, when the magnates assembled at Nottingham to hold a parliament there.  Isabella and Mortimer took up their abode in the castle, where Edward also resided.  Suspicions were abroad, and the castle was closely guarded by Mortimer’s Welsh followers.  Sir William Montague, a close friend of Edward’s,