Gwenwynwyn of Powys falls out with King John, who in October 1208 summons him to Shrewsbury, then arrests him and strips him of his lands; …

…Llywelyn takes the opportunity to annex southern Powys and northern Ceredigion and rebuild Aberystwyth castle.

Relations between Llywelyn and King John deteriorate in 1210.

J. E. Lloyd suggests that the rupture may have been due to Llywelyn forming an alliance with William de Braose, Fourth Lord of Bramber, who had fallen out with the king and had been deprived of his lands.

While John leads a campaign against de Braose and his allies in Ireland, an army led by Earl Ranulph of Chester and Peter des Roches, Bishop of Winchester, invades Gwynedd.

Llywelyn destroys his own castle at Deganwy and retreats west of the River Conwy.

The Earl of Chester rebuilds Deganwy, and Llywelyn retaliates by ravaging the earl's lands.

John sends troops to help restore Gwenwynwyn to the rule of southern Powys.

John invades Gwynedd in 1211 with the aid of almost all the other Welsh princes, planning according to Brut y Tywysogion "to dispossess Llywelyn and destroy him utterly".

The first invasion is forced to retreat, but in August John invades again with a larger army, crosses the River Conwy and penetrates Snowdonia.

Bangor is burnt by a detachment of the royal army and the Bishop of Bangor captured.

Llywelyn is forced to come to terms, and by the advice of his council sends his wife Joan to negotiate with the king, her father.

Joan is able to persuade her father not to dispossess her husband completely, but Llywelyn loses all his lands east of the River Conwy.

He also has to pay a large tribute in cattle and horses and to hand over hostages, including his illegitimate son Gruffydd, and is forced to agree that if he dies without a legitimate heir by Joan all his lands will revert to the king.

This is the low point of Llywelyn's reign, but he quickly recovers his position.

The other Welsh princes, who had supported King John against Llywelyn, soon become disillusioned with John's rule and change sides.

Llywelyn forms an alliance with Gwenwynwyn of Powys and the two main rulers of Deheubarth, Maelgwn ap Rhys and Rhys Gryg, and rises against John.

They have the support of Pope Innocent III, who has been engaged in a dispute with John for several years and has placed his kingdom under an interdict.

Innocent releases Llywelyn, Gwenwynwyn and Maelgwn from all oaths of loyalty to John and lifts the interdict in the territories which they control.

Llywelyn has been able to recover all Gwynedd, apart from the castles of Deganwy and Rhuddlan, within two months.

John plans another invasion of Gwynedd in August 1212.

According to one account, he had just commenced by hanging some of the Welsh hostages given the previous year when he received two letters.

One was from his daughter Joan, Llywelyn's wife, the other from William I of Scotland, and both warned him in similar terms that if he invaded Wales his magnates would seize the opportunity to kill him or hand him over to his enemies.

The invasion is abandoned.

Llywelyn takes the castles of Deganwy and …

…Rhuddlan in 1213.

Llywelyn, having made an alliance with Philip of France, now allies himself with the barons who are in rebellion against John, marching on Shrewsbury in 1215 and capturing it without resistance.

When John is forced to sign the Magna Carta, Llywelyn is rewarded with several favorable provisions relating to Wales, including the release of his son Gruffydd who has been a hostage since 1211.

The same year, Ednyfed Fychan is appointed seneschal of Gwynedd and is to work closely with Llywelyn for the remainder of his reign.

Llywelyn's influence is felt all across Wales as he aims to give substance to the long standing Aberffraw claim as the primary rulers of Wales.

The prince uses the structures of feudalism to strengthen his position, and …