Edward chose to renew the military conflict with the
Kingdom of Scotland in which his
father and
grandfather had engaged with varying success. Edward repudiated the
Treaty of Northampton that had been signed during the regency, thus renewing claims of English sovereignty over Scotland and resulting in the
Second War of Scottish Independence.
Intending to regain what the English had conceded, he won back control of
Berwick and secured a decisive English victory at the
Battle of Halidon Hill in 1333 against the forces of the infant
David II of Scotland. Edward III was now in a position to put
Edward Balliol on the throne of Scotland and claim a reward of 2,000 librates of land in the southern counties - the Lothians, Roxburghshire, Berwickshire, Dumfriesshire, Lanarkshire and Peebleshire. Despite the victories of Dupplin and Halidon, the Bruce party soon started to recover and by the close of 1335 and the
Battle of Culblean, the Plantagenet occupation was in difficulties and the Balliol party was fast losing ground.
At this time, in 1336, Edward III's brother
John of Eltham, Earl of Cornwall died.
John of Fordun's Gesta Annalia is alone in claiming that Edward killed his brother in a quarrel at
Perth.
Although Edward III committed very large armies to Scottish operations, by 1337 the vast majority of Scotland had been recovered by David II, leaving only a few castles such as Edinburgh, Roxburgh and Stirling in Plantagenet possession. These installations were not adequate to impose Edward's rule and by 1338/9 Edward had moved from a policy of conquest to one of containment.
Edward's military problems, however, were on two fronts; the challenge from the
French monarchy was of no less concern. The French represented a problem in three areas: first, they provided constant support to the Scottish through the
Franco-Scottish alliance. Philip VI protected David II in exile, and supported Scottish raids in
Northern England. Second, the French attacked several English coastal towns, leading to rumours in England of a full-scale invasion. Finally, the English king's possessions in France were under threat—in 1337, Philip VI confiscated the duchy of
Aquitaine and the county of
Ponthieu.
Instead of seeking a peaceful solution to the conflict by paying homage to the French king, Edward laid claim to the French crown as the only living male descendant of his deceased maternal grandfather, Philip IV. The French, however, invoked the
Salic law of succession and rejected the claim, pronouncing Philip IV's nephew, Philip VI, the true heir (
see below) and thereby setting the stage for the
Hundred Years' War.
In the war against France, Edward built alliances and fought by proxy through minor French princes. In 1338,
Louis IV named him vicar-general of the
Holy Roman Empire, and promised his support. These measures, however, produced few results; the only major military gain made in this phase of the war was the English naval victory at
Sluys on
24 June 1340, where 16,000 French soldiers and sailors died.
Meanwhile, the fiscal pressure on the kingdom caused by Edward's expensive alliances led to discontent at home. In response he returned unannounced on
30 November 1340. Finding the affairs of the realm in disorder, he purged the royal administration. These measures did not bring domestic stability, however, and a standoff ensued between the king and
John Stratford, the
Archbishop of Canterbury.
Edward, at the
Parliament of England of April 1341, was forced to accept severe limitations to his financial and administrative prerogatives. Yet, in October of the same year, the king repudiated this statute, and Archbishop Stratford was politically ostracised. The extraordinary circumstances of the 1341 parliament had forced the king into submission, but under normal circumstances the powers of the king in medieval England were virtually unlimited, and Edward took advantage of this.