Causes of the Hundred Years' War
Why Did England and France Go to War?
The Hundred Years’ War — the series of conflicts fought between England and France from 1337 to 1453 — did not begin from a single cause. It grew from decades of competing dynastic claims, disputed territories and diplomatic rivalries. Understanding why war broke out in 1337 requires looking at the interlinked pressures on both Edward III and the French Crown.
Edward III’s Claim to the French Throne
The most dramatic grievance was Edward III’s personal claim to the French throne. When the French king Charles IV died in 1328 without a male heir, Edward — as the son of Isabella of France and the grandson of Philip IV of France — argued he had the strongest dynastic claim to be the next king of France.
The French nobility rejected this argument. They invoked an ancient legal custom, the Salic law, which excluded inheritance through the female line. Instead, they crowned Philip of Valois as Philip VI. Edward initially accepted this — he paid homage to Philip for his French lands — but as relations deteriorated, he pressed his claim as a pretext for war.
Edward III claimed the French throne through his mother Isabella, daughter of Philip IV of France. When Charles IV died heirless in 1328, the French nobles rejected Edward’s claim and crowned Philip VI instead, planting a dynastic grievance that Edward later used to justify war.
The English Lands in France: Aquitaine
At the root of the conflict was the long-standing problem of English-held land in France. Since 1154, English kings had held territories in France, and by the fourteenth century Aquitaine in south-west France was the most important. It was extraordinarily profitable — the wine trade alone generated significant customs revenue — and English kings were determined to keep it.
But holding Aquitaine meant English kings were also feudal vassals of the French Crown for those lands — an awkward position when relations broke down. Philip VI repeatedly sought to undermine English control of Aquitaine, supporting local French lords who disputed English authority. In 1337, Philip formally confiscated Aquitaine, claiming Edward had failed in his feudal obligations. This act made war almost inevitable.
Aquitaine was not just a symbol of royal prestige — it was an economic asset. The region’s vineyards supplied a thriving wine trade with England, and the port of Bordeaux was one of the busiest in northern Europe. English merchants, traders and the Crown itself derived significant income from this commerce. Losing Aquitaine would have been a major financial as well as political blow to Edward III and his war-making capacity.
The Auld Alliance: France and Scotland
England’s strategic position was complicated by the Auld Alliance between France and Scotland. This alliance, which stretched back to 1295, meant that when England threatened France, Scotland would threaten England’s northern border — and vice versa. Edward III had already fought a war in Scotland in the 1330s to impose his preferred candidate, Edward Balliol, on the Scottish throne.
The Franco-Scottish alliance was therefore a genuine strategic threat. If Edward committed his forces to France, the Scots — backed by French support — could raid northern England. This forced Edward to maintain a military presence in the north even while fighting in France, stretching his resources considerably.
The Auld Alliance meant France and Scotland were mutual allies against England. While Edward III fought in France, Scotland — backed by French diplomacy and resources — could threaten England’s northern border, forcing Edward to fight on two fronts simultaneously.
Philip VI’s Role and the Confiscation of 1337
Philip VI was not a passive figure waiting to be attacked. He actively sought to weaken English power in France. He supported David II of Scotland against Edward’s preferred candidate, encouraged French lords in Aquitaine to resist English rule, and in May 1337 formally confiscated Aquitaine from Edward, declaring him a rebellious vassal.
This confiscation was the immediate trigger for the war. Edward III responded by formally declaring himself king of France in 1337 and launching a military campaign. The war that followed would last, with interruptions, until 1453 — long after Edward III himself was dead. But the causes laid down in the years before 1337 — dynastic rivalry, disputed territory, Scottish entanglement and French provocation — shaped every aspect of the conflict that followed.
Edward III’s aims were not simply to press his claim to the French throne — that may have been as much a propaganda device as a genuine ambition. His more immediate objectives were to secure Aquitaine against French encroachment, to end French support for Scotland, and to demonstrate his military prowess to the English nobility, who expected a king to lead his armies. War also offered the prospect of plunder, ransom and glory — incentives that mattered to the military class who would have to fight it.