Immediate causes of war Henry III died in 1272 and was succeeded by his son,
Edward I. Whereas Henry's ineffectiveness had led to the collapse of royal authority in England during his reign, Edward was a vigorous and forceful ruler and an able military leader. In 1274, tension between Llywelyn and Edward increased when
Gruffydd ap Gwenwynwyn of Powys and Llywelyn's younger brother
Dafydd ap Gruffydd defected to the English and sought Edward's protection. The continuing conflict with the Marcher Lords, particularly over Roger Mortimer's new castle at
Cefnllys, and Edward's harbouring of defectors led Llewelyn to refuse Edward's demand to come to
Chester in 1275 to do homage to him, as required by the
Treaty of Montgomery. For Edward, a further provocation came from Llywelyn's planned marriage to
Eleanor, daughter of
Simon de Montfort, the leader of a rebellion against the crown during the reign of Edward's father. In November 1276, Edward declared war on Llywelyn. However, his objective was to put down a recalcitrant vassal rather than to begin a war of conquest.
Invasion of 1277 Early in 1277, before the main royal army had been mustered, Edward deployed, in south and mid-Wales, a mixture of forces comprising paid troops, some of the marcher lords' retainers and knights of the royal household. They met with considerable success as many of the native Welsh rulers, resentful of Llywelyn's overlordship, surrendered and joined the English. From Chester the army marched into Gwynedd, camping first at
Flint and then
Rhuddlan and
Deganwy, most likely causing significant damage to the areas it advanced through. A fleet from the
Cinque ports provided naval support. Eastern Gwynedd was split between Edward and Llywelyn's brother Dafydd, with the remainder of the lands that had been tributary to him becoming effectively Edward's. Edward's victory was comprehensive and it represented a major redistribution of power and territory in Wales in Edward's favour. Edward now enjoyed a degree of direct control in the native Welsh areas which no previous English king had achieved. Dafydd launched a series of attacks co-ordinated with the Welsh rulers in
Deheubarth and
North Powys, who had been Llywelyn's vassals until 1277 and were now Edward's vassals. Llywelyn and the other Welsh leaders, including those in the south, joined in and it soon assumed a very different character from the 1277 campaign. It became a national struggle enjoying wide support among the Welsh, who were provoked particularly by Edward's attempts to impose
English law on the Welsh. Edward, however, soon began to see it as a war of conquest rather than just a punitive expedition to put down a rebellion. which marks the site of the Battle of Orewin Bridge The English launched a three-pronged attack, with Edward leading his army into North Wales along much the same route as in 1277,
Roger Mortimer operating in mid-Wales and the
Earl of Gloucester advancing with a substantial army in the south. Initially the Welsh were successful. In June 1282, Gloucester was defeated at the
Battle of Llandeilo Fawr. Edward replaced him with
William de Valence, Earl of Pembroke who raided in the south as far as
Aberystwyth but failed to engage with a Welsh army. However, the war turned in Edward's favour when Llywelyn unexpectedly marched out of North Wales towards
Builth in mid-Wales. He was lured into a trap and killed at the
Battle of Orewin Bridge on 11 December 1282. Taking advantage of this fortuitous event, Edward raised a new army and boldly marched into
Snowdonia in January 1283 and captured
Dolwyddelan Castle in the heartland of the Welsh resistance. Dafydd was taken to
Shrewsbury and executed as a traitor the following autumn. ==Aftermath==