The Cause of the Battle of Bannockburn
Edward II had last invaded Scotland in the years 1309 and 1310, but every time he rode north, the Scots seemed to disappear into their landscape after laying waste to everything in Edward's path. Therefore, without an army to fight and a lack of supplies from Bruce's scorched earth policy, the English army was forced to march back home again. These campaigns, like those his father waged before him, were very costly financially. In fact Edward was so broke that he couldn't even pay his troops.
This, of course, did not weigh very favourably with his barons. Many were already in opposition to the showering of affection, gifts and the title of the Earl of Cornwall on his favourite, Piers Gaveston, and the latest miserable state of financial affairs did nothing to strengthen Edward's hand against those who already saw him as a weak and inefficient ruler.
At the Parliament of 1311 it all came to a head, and the majority of his barons drew up a list of Ordinances - things they wanted changed about the way the country was run - and presented them to Edward. One of these Ordinances was that Gaveston should be sent into exile (again! He had already been exiled twice before). Edward raged and ranted against the imposition but in the end had no choice but to accept the barons' demands.
Gaveston was exiled to Flanders but returned secretly after three months, most probably to see his newborn daughter (but also, of course, to be with Edward!). When the barons heard of this, they turned on Edward and demanded that Gaveston be handed over to them and and put on trial for coming back to the realm illegally. Instead of bowing to their demands, Edward fled north and left Gaveston (who had become ill) at Scarborough castle while he rode south again to try to raise an army. While he was away, Gaveston surrendered to the earl of Pembroke who had promised that he would be safely conducted to London. While Pembroke was trying to be his usual honourable and moderate self, the earls of Lancaster, Warwick and Hereford had other ideas. On an overnight stop off, Pembroke left his prisoner with a guard while he visited his wife; Gaveston was seized by Warwick's men and taken to his castle. There he was given a summary trial and taken out to a piece of nearby land owned by Lancaster where he was beheaded.
A distraught and angry Edward vowed vengeance on those who had taken his beloved's life, creating worse fractures in the governance of the realm than there had been before.
In Scotland, Robert Bruce, who had had himself crowned king of that land in 1306, watched with interest as England's dysfunctional nobility shook itself apart. With Edward in a severely weakened position he had no fears of an imminent attack from England and so began to raid its northern borders with impunity, reaching as far as the Palatinate of Durham. The people of the borders, realising that there would be no help from their king, were forced into a 'truce' with Bruce, paying him 'protection money' not to attack them.
In the meantime, Bruce busied himself with retaking the strongholds that Edward still held in Scotland. Castle by castle, they fell to his surprise attacks or sieges. Once the castle was taken, Bruce gave orders for it to be destroyed so that it could not be manned against him by the English again. Throughout 1313-14, Bruce and his commanders took the town of Perth, and the castles of Roxburgh and Edinburgh. The oft disputed border town of Berwick, though, managed to hold out after a Scottish night attack was discovered when a dog started barking.
After the fall of Edinburgh castle, Bruce turned his attention to Stirling Castle - a formidable fortress important for its strategic position on the Roman road from England to Scotland. He entrusted its capture to his brother, Edward - an experienced general and veteran of many battles. However Stirling was built to withstand a long siege and Bruce lacked the siege weapons needed to bombard its walls. Realising this, Edward Bruce came to a truce with the castle's custodian, Philip Mowbray, that Mowbray would surrender the castle without a fight if it was not relieved by Edward II by 24th June the next year (1314). Philip de Mowbray was actually Scottish by birth, but during 1314, he was in service to the English. At the time of the truce, there was no question about his loyalty to the English crown, but he later defected to the Scots and died alongside Edward Bruce at the Battle of Faughart in 1318.
This chivalric agreement did not find favour at all with Robert Bruce, but the deal had been struck and now both sides had to make the best of it. Edward II meanwhile, had made his own truce with the rebel barons, even Lancaster and Warwick, and decided the time had come to go to war against Scotland again. Ostensibly this was to relieve the border lands from Bruce's oppression, but it was also to an opportunity to prove his strength as a king to those who had opposed him. After all, if he won a victory in Scotland, no-one would be able to criticise his rulership again. And so it was that Edward II and Robert Bruce started to prepare their respective armies for the coming clash at Midsummer.