After a disputed succession, Athelstan first sought to extend his influence circumspectly, purchasing Amounderness from Norse settlers, and allying himself by marriage with Sihtric, the Danish king of York. However, Sihtric died in 927, and Athelstan seized the opportunity to invade, occupying the kingdom of Northumbria. The kings of Scotland and Strathclyde promptly recognized his overlordship, which he then capped in 928 by accepting the formal submission of the kings of Wales. In 934, Athelstan launched an amphibious invasion of Scotland with his Danish and Welsh allies, marauding as far as Caithness. This campaign left the various regional powers in northern Britain smarting for revenge, and in 937, an army led by Constantine of Scotland and the Norse King of Dublin as far as York while and atypically complacent Athelstan “languished in sluggish leisure”. Eventually roused to action, Athelstan crushed the invaders at the battle of Brunanburh (937). Athelstan died in 939, but his half-brother Edmund restored control over the Midlands and Northumbria.