In June Henry marched northward to end the trouble from the Scots. With their usual policy the Scottish army under the Duke of Albany withdrew as the English crossed the border, and looked coolly on while Henry invested the castle of Edinburgh. The wants of his army forced him in fact to raise the siege; but even success would have been fruitless, for he was recalled by trouble nearer home. Wales was in full revolt. The country had been devoted to Richard; and so notorious was its disaffection to the new line that when Henry's son knelt at his father's feet to receive a grant of the Principality a shrewd bystander murmured, "He must conquer it if he will have it." The death of the fallen King only added to the Welsh disquiet, for in spite of the public exhibition of his body he was believed to be still alive. Some held that he had escaped to Scotland, and an impostor who took his name was long maintained at the Scottish Court. In Wales it was believed that he was still a prisoner in Chester Castle. But the trouble would have died away had it not been raised into revolt by the energy of Owen Glyndwr or Glendower. Owen was a descendant of one of the last native Princes, Llewelyn-ap-Jorwerth, and the lord of considerable estates in Merioneth. He had been squire of the body to Richard the Second, and had clung to him till he was seized at Flint. It was probably his known aversion from the revolution which had deposed his master that brought on him the hostility of Lord Grey of Ruthin, the stay of the Lancastrian cause in North Wales; and the same political ground may have existed for the refusal of the Parliament to listen to his prayer for redress and for the restoration of the lands which Grey had seized. But the refusal was embittered by words of insult; when the Bishop of St. Asaph warned them of Owen's power the lords retorted that " they cared not for barefoot knaves." They were soon to be made to care. At the close of 1400 Owen rose in revolt, burned the town of Ruthin, and took the title of Prince of Wales.

His action at once changed the disaffection into a national revolt. His raids on the Marches and his capture of Radnor marked its importance, and Henry marched against him in the summer of 1401. But Glyndwr's post at Corwen defied attack, and the pressure in the north forced the King to march away into Scotland. Henry Percy, who held the castles of North Wales as Constable, was left to suppress the rebellion, but Owen met Percy's arrival by the capture of Conway and the King was forced to hurry fresh forces under his son Henry to the west. The boy was too young as yet to show the military and political ability which was to find its first field in these Welsh campaigns, and his presence did little to stay the growth of revolt. While Owen's lands were being harried Owen was stirring the people of Caermarthen into rebellion and pressing the siege of Abergavenny; nor could the presence of English troops save Shropshire from pillage. Everywhere the Welshmen rose for their "Prince;" the Bards declared his victories to have been foretold by Merlin; even the Welsh scholars at Oxford left the University in a body and joined his standard. The castles of Ruthin, Hawarden, and Flint fell into his hands, and with his capture of Conway gave him command of North Wales. The arrival of help from Scotland and the hope of help from France gave fresh vigor to Owen's action, and though Percy held his ground stubbornly on the coast and even recovered Conway he at last threw up his command in disgust. A fresh inroad of Henry on his return from Scotland again failed to bring Owen to battle, and the negotiations which he carried on during the following winter were a mere blind to cover preparations for a new attack. So strong had Glyndwr become in 1402 that in June he was able to face an English army in the open field at Brynglas and to defeat it with a loss of a thousand men. The King again marched to the border to revenge this blow. But the storms which met him as he entered the hills, storms which his archers ascribed to the magic powers of Owen, ruined his army, and he was forced to withdraw as of old. A raid over the northern border distracted the English forces. A Scottish army entered England with the impostor who bore Richard's name, and though it was utterly defeated by Henry Percy in September at Homildon Hill the respite had served Owen well. He sallied out from the inaccessible fastnesses in which he had held Henry at bay to win victories which were followed by the adhesion of all North Wales and of great part of South Wales to his cause.

What gave life to these attacks and conspiracies was the hostility of France. The influence of the Duke of Burgundy was still strong enough to prevent any formal hostilities, but the war party was gaining more and more the ascendant. Its head, the Duke of Orleans, had fanned the growing flame by sending a format defiance to Henry the Fourth as the murderer of Richard. French knights were among the prisoners whom the Percies took at Homildon Hill; and it may have been through their intervention that the Percies themselves were now brought into correspondence with the court of France. No house had played a greater part in the overthrow of Richard, or had been more richly rewarded by the new King. But old grudges existed between the house of Percy and the house of Lancaster. The Earl of Northumberland had been at bitter variance with John of Gaunt; and though a common dread of Richard's enmity had thrown the Percies and Henry together, the new King and his powerful subjects were soon parted again. Henry had ground- indeed for distrust. The death of Richard left the young Mortimer, Earl of March, next claimant in blood of the crown, and the King had shown his sense of this danger by imprisoning the earl and his sisters in the Tower. But this imprisonment made their uncle, Sir Edmund Mortimer, the representative of their house; and Edmund withdrew to the Welsh Marches, refusing to own Henry for king. The danger was averted by the luck which threw Sir Edmund as a captive into the hands of Owen Glyndwr in the battle of Brynglas. It was natural that Henry should refuse to allow Mortimer's kinsmen to ransom so formidable an enemy; but among these kinsmen Henry Percy ranked himself through his marriage with Sir Edmund's sister, and the refusal served as a pretext for a final breach with the King.

Percy had withdrawn from the Welsh war in wrath at the inadequate support which Henry gave him; and his anger had been increased by a delay in repayment of the sums spent by his house in the contest with Scotland, as well as by the King's demand that be should surrender the Earl of Douglas whom he had taken prisoner at Homildon Hill. He now became the centre of a great conspiracy to place the Earl of March upon the thy-one. His father, the Earl of Northumberland, his uncle, Thomas Percy, the Earl of Worcester, joined in the plot. Sir Edmund Mortimer negotiated for aid from Owen Glyndwr; the Earl of Douglas threw in his fortunes with the confederates; and Henry Percy himself crossed to France and obtained promises of support. The war party had now gained the upper hand at the French court; in 1403 preparations were made to attack Calais, and a Breton fleet put to sea. At the news of its presence in the Channel Henry Percy and the Earl of Worcester at once rose in the north and struck across England to join Owen Glyndwr in Wales, while the Earl of Northumberland gathered a second army and advanced more slowly to their support. But Glyndwr was still busy with the siege of Caermarthen, and the King by a hasty march flung himself across the road of the Percies as they reached Shrewsbury. On the twenty-third of July a fierce fight ended in the defeat of the rebel force. Henry Percy was slain in battle, the Earl of Worcester taken and beheaded; while Northumberland, who had been delayed by an army under his rival in the north, Neville, Earl of Westmoreland, was thrown into prison, and only pardoned on his protestations of innocence. The quick, hard blow did its work. The young Earl of March betrayed the plans of his partisans to purchase pardon. The Breton fleet, which had defeated an English fleet in the Channel and made a descent upon Plymouth, withdrew to its harbors; and though the Duke of Burgundy was on the point of commencing the siege of Calais the plans of an attack on that town were no more heard of.

But the difficulty of Wales remained as great as ever. The discouragement of Owen at the failure of the conspiracy of the Percies was removed by the open aid of the French Court. In July, 1404, the French King in a formal treaty owned Glyndwr as Prince of Wales, and his promises of aid gave fresh heart to the insurgents. What hampered Henry's efforts most in meeting this danger was the want of money. At the opening of 1404 the Parliament grudgingly gave a subsidy of a twentieth, but the treasury called for fresh supplies in October, and the wearied Commons fell back on their old proposal of a confiscation of Church property. Under the influence of Archbishop Arundel the Lords succeeded in quashing the project, and a new subsidy was voted; but the treasury was soon as empty as before. Treason was still rife; the Duke of York, who had played so conspicuous a part in Richard's day as Earl of Rutland, was sent for a while to the Tower on suspicion of complicity in an attempt of his sister to release the Earl of March; and Glyndwr remained unconquerable.

But fortune was now beginning to turn. The danger from Scotland was suddenly removed. King Robert resolved to send his son James for training to the court of France, but the boy was driven to the English coast by a storm and Henry refused to release him. Had the Scots been friends, the King jested, they would have sent James to him for education, as he knew the French tongue quite as well as King Charles. Robert died of grief at the news; and Scotland fell into the hands of his brother, the Duke of Albany, whose one aim was that his nephew should remain a prisoner. James grew up at the English Court; and prisoner though he was, the excellence of his training was seen in the poetry and intelligence of his later life. But with its King as a hostage Scotland was no longer to be dreaded as a foe. France too was weakened at this moment; for in 1405 the long smouldering jealousy between the Dukes of Orleans and of Burgundy broke out at last into open strife. The break did little indeed to check the desultory hostilities which were going on. A Breton fleet made descents on Portland and Dartmouth. The Count of Armagnac, the strongest supporter of Orleans and the war party, led troops against the frontier of Guienne. But the weakness of France and the exhaustion of its treasury prevented any formal denunciation of the truce or declaration of war. Though Henry could spare not a soldier for Guienne Armagnac did little hurt. An English fleet repaid the ravages of the Bretons by harrying the coast of Brittany; and the turn of French politics soon gave Frenchmen too much work at home to spare men for work abroad. At the close of 1407 the murder of the Duke of Orleans by the order of the Duke of Burgundy changed the weak and fitful strife which had been going on into a struggle of the bitterest hate. The Count of Armagnac placed himself at the head of the murdered duke's partisans; and in their furious antagonism Armagnac and Burgundian alike sought aid from the English King.