Transferring operations to Aberdeenshire in late 1307, he threatened Banff before falling seriously ill, probably owing to the hardships of the lengthy campaign. Recovering, leaving John Comyn, 3rd Earl of Buchan unsubdued at his rear, Bruce returned west to take Balvenie and Duffus Castles, then Tarradale Castle on the Black Isle. Looping back via the hinterlands of Inverness and a second failed attempt to take Elgin, Bruce finally achieved his landmark defeat of Comyn at the Battle of Inverurie in May 1308; he then overran Buchan and defeated the English garrison at Aberdeen. The Harrying of Buchan in 1308 was ordered by Bruce to make sure all Comyn family support was extinguished. Buchan had a very large population because it was the agricultural capital of northern Scotland, and much of its population was loyal to the Comyn family even after the defeat of the Earl of Buchan. Most of the Comyn castles in Moray, Aberdeen and Buchan were destroyed and their inhabitants killed. In less than a year Bruce had swept through the north and destroyed the power of the Comyns who had held vice-regal power in the north for nearly one hundred years. How this dramatic success was achieved, especially the taking of northern castles so quickly, is difficult to understand. Bruce lacked siege weapons and it's unlikely his army had substantially greater numbers or was better armed than his opponents. The morale and leadership of the Comyns and their northern allies appeared to be inexplicably lacking in the face of their direst challenge. He then crossed to Argyll and defeated the isolated MacDougalls (allies of the Comyns) at the Battle of Pass of Brander and took Dunstaffnage Castle, the last major stronghold of the Comyns and their allies. Bruce then ordered harryings in Argyle and Kintyre, in the territories of Clan MacDougall