The treachery of the unprincipled English baron led to the desolation of Wales, to rivers of blood being shed, and to a good deal of humiliation to his master, Henry IV.
It may be remembered that when, in 1400, King Henry was preparing an expedition against Scotland, he summoned Glyndwr to join his forces, but confided the summons to Grey to deliver. Lord Grey purposely suppressed it, and then represented Owen to the King as a malcontent and a rebel; whereupon, without inquiry into the matter, Henry IV. pronounced his estate forfeit.
The Welsh had sympathised with Richard II., and they regarded Bolingbroke as a usurper, but would have contented themselves with singing dirges to the memory of Richard, had they not been exasperated to revolt by the violence and injustice of the Marchers. Owen, enraged against Grey de Ruthin, at first made a personal quarrel of his wrongs; but this soon developed and extended until it involved the whole of Wales, which rose against the English Crown.
In 1401 King Henry marched into North Wales, but the natives, and all those who held to Owen, retired into the mountains; and Henry returned to England, having effected nothing. He left Henry Prince of Wales, then a boy of thirteen, at Chester, to watch and control the Welsh, with Henry Hotspur, eldest son of the Earl of Northumberland, as Justice of North Wales and Constable of the Castles. Shakespeare has considerably disturbed men’s minds relative to persons and events of the period. He makes the fiery Percy but little older than Prince Hal, whereas he was actually older than Henry IV. And Prince Hal was by no means the roysterer at East Cheap as represented, but from early days engaged in war, and carrying on a prolonged contest with Glyndwr, a wily and able commander, in a country most difficult to hold.
Owen, finding that Harry Percy and the young prince were too strong to be attacked, now fell with all his force on South Wales, harrying the land of the English and of such Welsh as would not join him. Then he abruptly turned to the Severn valley, burnt Montgomery, and was only stopped under the red walls of the castle of Percy at Welshpool. Now all Wales was in insurrection, and everywhere Owen was regarded as one who would deliver the Cymry from their hereditary oppressors. The rapid progress of his army spread terror along the Marches, and messengers on swift horses galloped to London to announce to the King that unless succour were sent his castles would fall.
In October, 1401, King Henry and the Prince of Wales entered the Principality at the head of a huge army, and pushed on to Bangor, only to find that the Welsh had retreated to the mountains, carrying off with them all their goods. The King passed along the coast to the abbey of Strata Florida in Cardiganshire, which he gave up to pillage and fire. Having succeeded in capturing about a thousand Welsh children without having fought a battle, Henry ingloriously withdrew.
About this time, moreover, Owen succeeded in getting hold of his great enemy Lord Grey de Ruthin, and sent him to his tower of Dolbadarn, there to languish until he could raise the heavy ransom which Owen, who was sorely in want of money, demanded for his release.
Henry Percy, unable to obtain payment for his services in Wales, and reimbursement for large sums laid out by himself in the King’s service, threw up his charge and retired to Northumbria to fight the Scots.
In May, 1402, Owen Glyndwr attacked the Welsh territories of young Edmund Earl of March, who, with his younger brother Roger, was held in custody by the King, on account of his having been acknowledged by Parliament to be the lineal heir to King Richard.
Sir Edmund Mortimer, their uncle and guardian, hastened to protect the lands, assisted by the other Marchers.