found it easy to extend it over most of Wales, because the rule of
the English officials made the Welsh chiefs long for the protection
of Gwynedd. The Barons' War paralysed the power of the King, and
Llywelyn made an alliance with Simon de Montfort and the barons.
Even after Montfort's fall in 1265 the barons were so powerful that
the King was still at their mercy. In 1267 Llywelyn's position as
Prince of Wales was recognised in the Treaty of Montgomery. His sway
extended from Snowdon to the Dee on the east, and to the Teivy and
the Beacons on the south--practically the whole of modern Wales,
except the southern seaboard. Within these wide bounds all the Welsh
barons were to swear fealty to Llywelyn, the only exception being
Meredith ap Rees of Deheubarth.

The second struggle of Llywelyn's reign took place between 1267 and
1277. He tried to weld his land into a closer union, and many of the
chiefs of the south and east became willing to call in the English
King. Two of them, his own brother David and Griffith of Powys, fled
to England, and were received by Edward, who had been king since
1272. Llywelyn and Edward distrusted each other. Edward wished to
unite Britain in a feudal unity, and to crush all opponents.
Llywelyn thought of helping the barons; he might become their leader.
Eleanor, the daughter of Simon de Montfort, the old leader of the
barons, was betrothed to him. War broke out. The barons--Clares and
Mortimers, and all--joined the King. Llywelyn's dominions were
invaded at all points, his barons had to yield, one after the other;
and finally, in 1277, Llywelyn had to accept the Treaty of Rhuddlan.
His dominions shrunk to the old limits of Snowdon, his sway over the
rest of Wales was taken from him, and the title of Prince of Wales
was to cease with his life.