Llywelyn's power declined over the next two decades. In 1276 Henry's son, Edward I, invaded Wales following a dispute with the prince, breaking his power in South Wales, and in 1282 Edward's second campaign resulted in Llwelyn's death and the collapse of independent Welsh rule. Further defences were added to the walls until work stopped around 1290. Local disputes remained. De Clare argued with Humphrey de Bohun, the earl of Hereford, in 1290 and the following year the case was brought before the king, resulting in the temporary royal seizure of Caerphilly.