External troubles continued to multiply during Henry's earlier years. The Scots had declared war, and there was every sign that the French would soon follow suit, for the king's failure to crush Glendower had destroyed his reputation for capacity. The rebel achieved his greatest success in June 1402, when he surprised and routed the whole levy of the marcher lords at Bryn G'las, between Pilleth and Knighton, capturing (among many other prisoners) Sir Edmund Mortimer, the uncle and guardian of the young earl of March, whom all malcontents regarded as the rightful monarch of England. A few months after the king's fortune seemed to take a turn for the better, when the Scots were defeated at Homildon Hill by the earl of Northumberland and his son Henry Percy, the celebrated "Hotspur." But this victory was to be the prelude to new dangers: half the nobility of Scotland had been captured in the battle, and Northumberland intended to fill his coffers with their ransoms; but the king looked upon them as state prisoners and announced his intention of taking them out of the earl's hands. Northumberland was a greedy and unscrupulous Border chief, who regarded himself as entitled to exact whatever he chose from his master, because he had been the first to join him at his landing in 1399, and had lent him a consistent support ever since. He had been amply rewarded by grants of land and money, but was not yet satisfied. In indignation at the first refusal that he had met, the earl conspired with Glendower to raise rebellion in the name of the rightful heirs of King Richard, the house of March. The third party in the plot was Sir Edmund Mortimer, Glendower's captive, who was easily persuaded to join a movement for the aggrandizement of his own family. He married Owen's daughter, and became his trusted lieutenant. Northumberland also enlisted the services of his chief Scottish prisoner, the earl of Douglas, who promised him aid from beyond Tweed. Insurrection in the north and west. Defeat of the rebels at Shrewsbury.