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. In South Wales, Henry gradually extended his authority across the region, but the campaigns were not pursued with vigour and the King did little to stop the Marcher territories along the border becoming increasingly independent of the Crown. In 1256, Llywelyn ap Gruffudd rebelled against Henry and widespread violence spread across Wales. Henry promised a swift military response but did not carry through on his threats. Ireland was important to Henry, both as a source of royal revenue – an average of £1,150 was sent from Ireland to the Crown each year during the middle of his reign – and as a source of estates that could be granted to his supporters. The major landowners looked eastwards towards Henry's court for political leadership, and many also possessed estates in Wales and England. The 1240s saw major upheavals in land ownership due to deaths among the barons, enabling Henry to redistribute Irish lands to his supporters. In the 1250s, the King gave out numerous grants of land along the frontier in Ireland to his supporters, creating a buffer zone against the native Irish. The local Irish kings began to suffer increased harassment as English power increased across the region. These lands were in many cases unprofitable for the barons to hold and English power reached its zenith under Henry for the medieval period. In 1254, Henry granted Ireland to his son, Edward, on condition that it would never be separated from the Crown. Henry maintained peace with Scotland during his reign, where he was the feudal lord of Alexander II. Henry assumed that he had the right to interfere in Scottish affairs and brought up the issue of his authority with the Scottish kings at key moments, but he lacked the inclination or the resources to do much more. Alexander had occupied parts of northern England during the First Barons' War but had been excommunicated and forced to retreat. Alexander married Henry's sister Joan in 1221, and after he and Henry signed the Treaty of York in 1237, Henry had a secure