History is messy. We like to think of wars starting because of one big event, like an assassination or a surprise invasion, but the reality is usually a slow-motion car crash of egos, bad luck, and legal loopholes. If you want to understand what caused the Hundred Years War, you have to look past the dates in your old school textbooks. It wasn't just one thing. It was a 116-year-long family feud that spiraled out of control because a few medieval kings couldn't share.
Basically, the whole thing was a massive legal dispute over who owned what and who had to bow to whom. Imagine your neighbor claims your backyard belongs to them because their great-grandmother once lived there, but you’ve been paying the mortgage for decades. Now add knights, longbows, and the fate of Western Europe to that scenario. That’s the Hundred Years War in a nutshell.
The King Who Ran Out of Sons
The fuse was actually lit in 1328 when King Charles IV of France died. He didn't have an heir. No sons, no brothers, nothing. This was a huge problem because the French crown was the ultimate prize in Europe.
At the time, the closest male relative was actually Edward III of England. His mother, Isabella, was Charles IV’s sister. On paper, it seemed simple: Edward should be King of France and England. But the French nobility hated that idea. They didn't want a "foreigner" sitting on their throne, especially not an English one. They dug through ancient legal texts and found something called the Salic Law.
This old rule basically said that the throne couldn't be inherited through a woman. It was a convenient excuse to bypass Edward and give the crown to Philip VI of Valois, Charles’s cousin. Philip was "fully French," and the locals liked him better. This snub is a massive part of what caused the Hundred Years War because it gave the English kings a permanent legal claim they could use whenever they wanted to pick a fight.
Edward III didn't start a war immediately. He was young, and he had his own problems back home in England. He actually did homage to Philip VI at first, basically admitting Philip was the boss of certain lands. But that didn't last.
A Patchwork of Land and Ego
To understand the tension, you have to look at a map of medieval France. It wasn't one unified country like it is today. It was more like a collection of powerful duchies. The English kings weren't just kings of England; they were also the Dukes of Aquitaine (a huge chunk of southwest France).
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This created a bizarre situation.
As King of England, Edward III was an independent sovereign. But as Duke of Aquitaine, he was technically a "vassal" to the King of France. He was supposed to kneel and swear loyalty to Philip. It was humiliating. Every time the French king wanted to exert power, he would interfere in Aquitaine’s legal business or demand more taxes.
Philip VI was also a bit of a bully. He started nibbling away at the edges of Edward's French lands. By 1337, Philip had had enough of Edward’s stalling and declared that Aquitaine was "forfeited" back to the French crown. That was the point of no return. Edward responded by re-asserting his claim to the entire French throne. He wasn't just a duke anymore; he was, in his own mind, the rightful King of France.
The Scottish Problem and the "Auld Alliance"
We often forget that Scotland played a huge role in what caused the Hundred Years War. It’s the classic "the enemy of my enemy is my friend" scenario.
France and Scotland had a pact called the Auld Alliance. Whenever England tried to invade Scotland, France would help the Scots. Whenever England looked like it was getting too powerful in France, the Scots would raid northern England to distract them.
In the years leading up to 1337, Philip VI was actively protecting David II of Scotland, who was an enemy of Edward III. Philip even gathered a fleet of ships to help the Scots. Edward realized that as long as France was powerful and meddling, he would never be secure in England. He had to take the fight to the continent to protect his own backyard.
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Wool, Cash, and the Flemish Connection
Wars aren't just about crowns and honor; they’re about money. Always.
The County of Flanders (modern-day Belgium) was the industrial heart of Europe back then. They produced the high-quality cloth that everyone wanted. But they needed English wool to make it. England’s economy was basically built on sheep.
The French kings tried to exert control over Flanders, which threatened the English wool trade. If the French took over Flanders, they could bankrupt Edward III by cutting off his biggest customer. The Flemish merchants were stuck in the middle. They didn't want to rebel against their French overlords, but they couldn't survive without English wool. Eventually, they pressured Edward to declare himself King of France so they could legally "switch sides" and support him without technically being traitors to the French crown.
Why the Conflict Didn't Just End
The reason this war lasted for over a century instead of being a quick skirmish comes down to the nature of medieval warfare. It wasn't one long battle. It was a series of raids (called chevauchées), long periods of truce, and occasional massive battles like Crécy and Agincourt.
The English had a technological advantage with the longbow. It was the "machine gun" of the Middle Ages. A skilled archer could fire 10 to 12 arrows a minute. When the French knights tried to charge, they were turned into pincushions before they even got close.
But even with these victories, the English didn't have the manpower to occupy all of France. They would win a battle, take some land, and then run out of money or get hit by the Black Death. Both sides were constantly going broke. In fact, Edward III had to borrow so much money from Italian bankers (the Bardi and Peruzzi families) that he eventually defaulted, causing a massive financial crisis in Florence.
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Debunking the Myths
One thing people get wrong about what caused the Hundred Years War is the idea that it was a "nationalist" war. In 1337, the people living in Aquitaine didn't necessarily feel "French" or "English." They were subjects of a lord.
The concept of a "country" as we know it today was actually a result of the war, not the cause of it. By the time Joan of Arc showed up in the 1420s, a sense of French national identity had started to form. Before that, it was mostly just aristocrats arguing over property rights and family trees.
Another misconception is that it was 100 years of constant fighting. Honestly, most of the time was spent waiting. Waiting for the plague to pass, waiting for a king to grow up, or waiting for enough money to pay the mercenaries. There were gaps of 20 years where almost nothing happened.
A Quick Timeline of the Spiral
- 1328: Charles IV of France dies. Philip VI takes the throne.
- 1333: France supports Scotland against England, infuriating Edward III.
- 1336: Edward III bans wool exports to Flanders to pressure them.
- 1337: Philip VI "confiscates" Aquitaine. The war officially begins.
- 1340: Edward III officially calls himself "King of France" for the first time.
Insights for Understanding Modern Conflict
If you look at the roots of this war, you see patterns that still happen today.
- Proxies Matter: The war in Scotland was the "proxy war" that made a larger conflict inevitable. Modern geopolitics works the same way.
- Economic Interdependence: The wool trade in Flanders shows how trade can force a country's hand into a war they might not want.
- Legalism as a Weapon: The use of the Salic Law shows how leaders use "legality" to justify actions they were going to take anyway for power.
To truly understand what caused the Hundred Years War, you have to stop looking for a single villain. It was a perfect storm of a dying dynasty, a broken feudal system, and an economic crisis.
If you want to dig deeper into how this changed the world, look at the evolution of the English Parliament. Because Edward III was always broke from fighting in France, he had to keep asking his nobles for money. In exchange, they demanded more power. The war that was meant to make the King of England more powerful actually ended up giving more power to the people.
To see this history in person, a visit to the castles of the Loire Valley or the battlefields of Normandy offers a haunting look at where these egos clashed. You can still see the scars on the walls of places like Château de Vincennes, where the French kings tried to hold their world together while it was falling apart.