In making this alliance the Scots took the only step possible; for they had no choice between fighting England with France as their ally, or fighting France as the subjects of King Edward. The contest which was approaching seemed all but hopeless. The population of England was six times as large as that of Scotland, and Edward could draw from Ireland and Wales great numbers of troops. The English were trained to war by constant fighting in France, Ireland, and Wales; while the Scots had, for a very long period, enjoyed a profound peace, and were for the most part wholly ignorant of warfare.

Edward at once prepared to invade Scotland; in January he seized the lands owned by Comyn in Northumberland and sold them, directing the money to be applied to the raising and maintenance of 1000 men-at-arms and 60,000 foot soldiers, and in February issued a writ for the preparation of a fleet of 100 vessels.

On the 25th of March he crossed the Tweed with 5000 horse and 30,000 foot. The Scotch leaders were, of course, aware of the gathering storm, and, collecting their forces, attempted a diversion by crossing the Border to the west and making a raid into Cumberland. King Edward, however, marched north and besieged Berwick, the richest and most flourishing of the towns of Scotland. With the exception of the castle, it was weakly fortified. The attack was commenced by the fleet, who were, however, repulsed and driven off. A land assault, led by the king in person, was then made; the walls were captured, and the town completely sacked. The inhabitants were butchered without distinction of age, sex, or condition, and even those who fled to the churches were slain within the sanctuary. Contemporary accounts differ as to the numbers who perished on this occasion. Langtoff says 4000; Hemingford, 8000; Knighton, another English writer, says 17,000; and Matthew of Westminster, 60,000. Whichever of these writers is correct, it is certain that almost the whole of the men, women, and children of the largest and most populous Scottish town were butchered by the orders of the English king, who issued direct orders that none should be spared. From this terrible visitation Berwick, which was before called the Alexandria of the West, never recovered. The castle, which was held by Sir William Douglas, surrendered immediately; and Sir William, having sworn fealty to the English king, was permitted to depart.