The death of King Alexander III, and subsequently that of his heir Margaret in 1290, weakened Scotland considerably, and gave Edward I of England the opportunity to exercise power over this apparently subsidiary country. The two main claimants to the throne were John Balliol and Robert Bruce, Lord of Annandale (grandfather of the more famous Robert the Bruce). Their rival claims were determined by a group of Scottish auditors, presided over by Edward I of England, and they declared Balliol as King on 17 November 1292.
Edward I, however, was not prepared to give up his overseeing power in Scotland to King John once he had taken the throne. He launched an English invasion, and took Dunbar Castle in April 1296. John Balliol, …
Editors. "Reign of King Edward I of Scotland". The Literary Encyclopedia. First published 31 July 2012
[http://www.litencyc.com/php/stopics.php?rec=true&UID=615, accessed 29 March 2017.]