Dissensions among the barons, caused by the weakness and absence of the Crown, were one great cause of the decline of the colony. Another was the policy of Edward I., which left him little time to attend to Ireland, and tempted him constantly to draw supplies of men from thence. A third was the battle of Bannockburn, which allowed victorious Scotland to compete with England for the dominion of the neighbouring island; and the Irish themselves were not slow to adopt the principle that England's difficulty is Ireland's opportunity. In 1315 Edward Bruce landed near Larne with 6,000 men, including some of the best knights in Scotland. Having been joined by O'Neill and the chiefs depending on him, Bruce twice defeated the Red Earl of Ulster, occupied the strongholds of Down and Antrim, and wintered in Westmeath. In the spring he overthrew the Viceroy, Sir Edmund Butler, at Ardscull, for the Earl of Ulster disdained to serve under the King's representative, and the English armies were therefore beaten in detail. Bruce gained another battle at Kells, wasted all northern Leinster, and then returned to Carrickfergus, where he was joined by King Robert with reinforcements. The Scots went almost where they liked, and Robert Bruce is said to have heard mass at Limerick on Palm Sunday, 1317. They did not cross the Shannon, and seem not to have gone further south than Cashel. Dublin was not attacked, though the invaders came as near as Castleknock. On Easter Thursday, 1317, Roger Mortimer landed at Youghal with 15,000 men and full viceregal powers, and the Bruces retired before him into Ulster. They had devastated the country, and lost many men from the famine which they themselves had caused. [Sidenote: The Bruces fail to conquer Ireland.]