Edward the Elder was succeeded by his son Æthelstan, who Keynes calls the "towering figure in the landscape of the tenth century". His victory over a coalition of his enemies – Constantine, King of the Scots; Owain ap Dyfnwal, King of the Cumbrians; and Olaf Guthfrithson, King of Dublin – at the battle of Brunanburh, celebrated by a poem in the "Anglo-Saxon Chronicle", opened the way for him to be hailed as the first king of England. Æthelstan's legislation shows how the king drove his officials to do their respective duties. He was uncompromising in his insistence on respect for the law. However this legislation also reveals the persistent difficulties which confronted the king and his councillors in bringing a troublesome people under some form of control. His claim to be "king of the English" was by no means widely recognised. The situation was complex: the Hiberno-Norse rulers of Dublin still coveted their interests in the Danish kingdom of York; terms had to be made with the Scots, who had the capacity not merely to interfere in Northumbrian affairs, but also to block a line of communication between Dublin and York; and the inhabitants of northern Northumbria were considered a law unto themselves. It was only after twenty years of crucial developments following Æthelstan's death in 939 that a unified kingdom of England began to assume its familiar shape. However, the major political problem for Edmund and Eadred, who succeeded Æthelstan, remained the difficulty of subjugating the north. In 959 Edgar is said to have "succeeded to the kingdom both in Wessex and in Mercia and in Northumbria, and he was then 16 years old" (ASC, version 'B', 'C'), and is called "the Peacemaker". By the early 970s, after a decade of Edgar's 'peace', it may have seemed that the kingdom of England was indeed made whole. In his formal address to the gathering at Winchester the king urged his bishops, abbots and abbesses "to be of one mind as regards monastic usage . . . lest differing ways of observing the customs of one Rule and one country should bring their holy conversation into disrepute".