Andrew Harclay, 1st Earl of Carlisle the Scots, under the command of Robert the Bruce, at the Battle of Old Byland in Yorkshire. The English commander, John of Brittany, Earl of Richmond, was taken prisoner, while the king himself barely escaped capture. It was the worst defeat the English had suffered in the wars since the Battle of Bannockburn in 1314. Harclay had received a summons to join the royal army, but had not been able to bring his troops south in time to come to the king's rescue. The event convinced him that the war against Scotland could not be won under the leadership of
Robert the Bruce planned a major military campaign with the support of Lancaster and the barons, mustering a large army of between 15,000 and 20,000 men. In the spring of 1314, Edward Bruce laid siege to Stirling Castle, a key fortification in Scotland whose governor, Philip de Mowbray, agreed to capitulate if not relieved before 24 June 1314. In March, James Douglas captured Roxburgh, and Randolph captured Edinburgh Castle, while in May, Bruce again raided England and subdued the Isle of Man. News of the agreement regarding Stirling Castle reached the English king in late May, and he decided to speed his march