Of all Edward's policies nothing affected the country more continuously than his wars. From his accession to 1323 England was at war with Scotland. Except for the final repelling of a Scottish invasion of Ireland in 1318, there was one long series of disasters. The Scots, led by their able leader Robert Bruce, retained the initiative most of the time. The English policy of trying to defend a chain of castles inside Scotland and on the frontier did not work, as the Scots gradually recaptured the key strongholds. They managed to organise raids deep into English territory and reduced the counties south of the border to abject terror and deep misery. The few English attempts to stage massive counter-invasions ended either in crushing military defeats, as happened at Bannockburn in 1314, or in frustrating failures brought about by the harassing tactics of the Scots and the lack of supplies for Edward's troops. After Edward finally concluded a prolonged truce with the Scots in 1323, he blundered later that year into a war with France that finally destroyed him.

Until 1322 Edward's warlike enterprises were hampered by a chronic shortage of money, though this was not the main cause of his military failures. Thereafter he was so rich that even enormous expenditures on war did not exhaust his large reserves, which at the time of his fall from power in late October 1326 still amounted to at least a year's revenue.