Military history of Scotland for Robert I's success was his ability to call on naval forces from the Islands. As a result of the expulsion of the Flemings from England in 1303, he gained the support of a major naval power in the North Sea. The development of naval power allowed Robert to successfully defeat English attempts to capture him in the Highlands and Islands and to blockade major English controlled fortresses at Perth and Stirling, the last forcing Edward II to attempt the relief that resulted at English defeat at Bannockburn in 1314. Scottish naval forces allowed invasions of the Isle of Man
Battle of Bannockburn was reopened. After the death of Edward I, his son Edward II of England came to the throne in 1307 but was incapable of providing the determined leadership his father had shown, and the English position soon became more difficult. In 1313, Bruce demanded the allegiance of all remaining Balliol supporters, under threat of losing their lands, as well as the surrender of the English forces encircling Stirling Castle. The castle was one of the most important castles held by the English, as it commanded the route north into the Scottish Highlands. It was besieged in 1314 by Robert the