who affirmed their homage and allegiance to Llywelyn. Beverley Smith comments: "The leader in military alliance assumed the role of lord, his erstwhile allies were now his vassals." Gwenwynwyn of Powys changed sides again that year and allied himself with King John. Llywelyn called up the other princes for a campaign against him and drove him out of southern Powys once more. Gwenwynwyn died in England later that year, leaving an underage heir. King John also died that year, and he also left an underage heir in King Henry III with a minority government set up in England. In 1217, Reginald de Braose of Brecon and Abergavenny, who had been allied to Llywelyn and married his daughter, Gwladus Ddu, was induced by the English crown to change sides. Llywelyn responded by invading his lands, first threatening Brecon, where the burgesses offered hostages for the payment of 100 marks, then heading for Swansea where Reginald de Braose met him to offer submission and to surrender the town. He then continued westwards to threaten Haverfordwest where the burgesses offered hostages for their submission to his rule or the payment of a fine of 1,000 marks. Treaty of Worcester and border campaigns 1218–1229 Following King John's death Llywelyn concluded the Treaty of Worcester with his successor Henry III in 1218. This treaty confirmed him in possession of all his recent conquests. From then until his death Llywelyn was the dominant force in Wales, though there were further outbreaks of hostilities with marcher lords, particularly the Marshall family and Hubert de Burgh, and sometimes with the king. Llywelyn built up marriage alliances with several of the Marcher families. One daughter, Gwladus Ddu, ("Gwladus the Dark") was already married to Reginald de Braose of Brecon and Abergavenny, but with Reginald an unreliable ally Llywelyn married another daughter, Marared, to John de Braose of Gower, Reginald's nephew. He found a loyal ally in Ranulph, Earl of Chester, whose nephew and heir, John the Scot, married Llywelyn's daughter Elen in about 1222. Following Reginald de Braose's death in 1228, Llywelyn also made an alliance with the powerful Mortimer family of Wigmore when Gwladus Ddu married as her second husband Ralph de Mortimer. Llywelyn was careful not to provoke unnecessary hostilities with the crown or the Marcher lords; for example in 1220, he compelled Rhys Gryg to return four commotes in South Wales to their previous Anglo-Norman owners.