Henry's position in Wales was strengthened during the first two decades of his personal rule. Following the death of Llywelyn the Great in 1240, Henry's power in Wales expanded. Three military campaigns were carried out in the 1240s, new castles were constructed and the royal lands in the County of Chester were expanded, increasing Henry's dominance over the Welsh princes. Dafydd, Llywelyn's son, resisted the incursions, but died in 1246, and Henry confirmed the Treaty of Woodstock the following year with Owain and Llywelyn ap Gruffudd, Llywelyn the Great's grandsons, under which they ceded land to the King but retained the heart of their princedom in Gwynedd.