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.