Llywelyn ap Gruffudd declared himself ruler of North Wales and had given himself the title of Prince of Wales. King Henry III told Prince Edward that he would not help remove Llywelyn from power and Edward would have to do that himself if he wanted his inheritance.

Under their leader, Llywelyn ap Gruffydd, the Welsh invaded the northern coastal areas that had agreed to English rule. Prince Edward, who had been given the areas to administer himself by his father Henry III asked his father for help but Henry refused.

Henry III relented to his son's demands for assistance to fight the Welsh, and joined him on a campaign to retake the territories lost to the Welsh under Llywelyn.

Llywelyn received the support of the native lords in Wales and declared himself the 'Prince of Wales'. Under him, a united Welsh nation was ready to defend itself from the English.

Llywelyn ap Gruffydd, the 'Prince of Wales' attacked the castle at Tenby.

The Treaty of Shrewsbury was an agreement between King Henry III of England and Llywelyn the Prince of Wales. Henry recognised Llywelyn's position as Prince of Wales in return for a regular payment. Also known as the Treaty of Montgomery.

Llywelyn ap Gruffydd of Wales had consistently failed to do homage to King Edward I. He had been paying sums of money to the English crown as agreed in the Treaty of Shrewsbury drawn up in 1267 but after the death of Henry III the payments had stopped. Edward's repeated demands for a meeting with Llywelyn were ignored. In an attempt to stir up internal problems in England Llywelyn sent to France for Eleanor de Montfort who had been promised to him as a bride for his support of Henry III in the Baronial revolt against the English King. Eleanor was captured by the English on the journey and was then held prisoner by Edward. Edward finally had to accept Llywelyn as a rebel and so began his war on the Welsh. Feudal levies were called for in June 1277 allowing an army to be raised via the feudal system to supports the King's war with the Welsh.

Before the main army could be assembled Edward ordered that the Marchers and the smaller permanent forces attached to the royal household were to be sent out in three detachments. Although not much headway was made in the north the south and central districts abandoned their allegiance to Llywelyn. Roger Mortimer was able to force Llywelyn to retreat from Powys northwards. It was soon clear that the only area the Llywelyn had any control over was the north of Wales.

Reconstruction of the castle at Aberystwyth was begun by the English during Edward I's conflict with Llywelyn ap Gruffydd.

King Edward I of England granted Ruthin to Dafydd, the brother of Prince Llewelyn ap Gruffudd in return for his help against his brother who have been attacking English interests in the north of Wales. Construction of Ruthin Castle may have begun under the direction of Edward or Dafydd himself.

Edward I called for feudal levies to be collected to pay for his war against the Welsh prince who had repeatedly refused to pay him homage.

Llywelyn was cut off from supplies and an escape route so had to accept defeat. Edward demanded payment of £50,000 and all of Llywelyn's territories. Llywelyn was left only with the Isle of Anglesey which he had to pay rent of £1,000 a year. Edward also demanded that Anglesey should be handed over if Llywelyn died without a male heir. Llywelyn swore fealty to Edward at Rhuddlan on November 10th and again at a ceremony at Westminster Abbey on Christmas Day.

With peace between Edward and Llywelyn, the marriage between Llywelyn and Eleanor de Montfort was allowed to continue. The marriage took place at Worcester and was attended by Edward.

David, Llywelyn's brother, rose up in revolt. Llywelyn, even though he had sworn fealty to Edward, joined his brother in the fight against the English.

Luke de Tany, on the side of the English, had taken control of Anglesey. The plan was attack the Welsh rebels from the north and so a bridge of boats was constructed across the Menai Straits that separate Anglesey from Wales. The Welsh were waiting for the English in force and the English plan failed. Many of the English knights drowned when the boat bridge was destroyed.

Whilst fighting in the south of Wales Llywelyn was killed. He had moved to the rear of his army feeling secure with the way the war was progressing. A detachment of English found a way across the river Wye which Llywelyn was using for protection and moved around the rear of the Welsh army where the Prince was. Before Llywelyn could rejoin his army he was cut down and killed. His head was cut off and taken to the King Edward. Llywelyn's brother David carried on the fight against the English for another six months.

After the death of Lleweyln Edward was free to occupy all the previous strongholds of the Welsh Princes. In 1283 Edward attacked and captured the Welsh castle at Dolyyddlan.