Hundred Years' War
The 116-year English attempt to take the French throne, which England lost, and which turned two feudal kingdoms into rival nation-states.
From 1337 to 1453 the kings of England fought to take the throne of France, and lost. The fighting was not continuous. It came in campaigns separated by truces and dynastic bargaining, spread over 116 years, and both countries were changed far more by the war itself than by anything that ended up on the map.
The legal argument began with a succession problem. When the direct male line of French kings ran out in 1328, the crown went to a cousin, Philip VI. Edward III of England, whose mother was a French princess, claimed it through her, and French lawyers ruled that the crown could not pass through a woman. The practical trigger came in 1337, when Philip confiscated Gascony, the wine-exporting province in southwest France that Edward held as a vassal of the French king.
The English century
For decades the English won the battles. At Crecy in 1346 and Poitiers in 1356, dismounted English men-at-arms and massed longbowmen destroyed much larger French armies of mounted knights. At Poitiers they captured King John II of France and held him for a ransom so large it was never fully paid. The Treaty of Bretigny in 1360 handed Edward about a third of France outright.
France then recovered by refusing to fight. Bertrand du Guesclin avoided open battle, took territory back town by town, and by 1380 had reversed most of the English gains.
Henry V restarted the war and won at Agincourt in 1415 against an army several times the size of his own. The Treaty of Troyes in 1420 disinherited the French heir and made Henry the next king of France. He died of dysentery in 1422, a few weeks before the French king he was due to succeed.
How France won
The turn came in 1429, when a teenage farm girl from Lorraine talked her way into the French court, was sent with a relief force to besieged Orleans, and broke the siege in nine days. Joan of Arc had Charles VII crowned at Reims, the traditional coronation city, which turned a disputed claimant into an anointed king. She was captured, sold to the English, and burned as a heretic in 1431. The damage she had done was permanent.
The decisive blow was diplomatic. Burgundy, the powerful French duchy that had been fighting alongside the English, switched sides in 1435, and England lost its base on the continent. France then built the thing England could not afford: a permanent tax, the taille, which paid for the first standing companies of professional cavalry in 1445 and for an artillery train run by the Bureau brothers that was the best in Europe. At Formigny in 1450 and Castillon in 1453, French cannon broke English armies in the field. England was left holding Calais, and lost that in 1558.
What the war left behind
France emerged with permanent taxation, a standing army, and a monarchy that had absorbed its greatest provinces. That is the state Louis XIV would inherit. England, pushed off the continent, turned toward the sea, and its ruling class stopped speaking French.
Both countries also came out of it with something new: the sense that the enemy was a foreign people rather than a rival family. And the defeated English lords came home with private armies and grievances. Two years after Castillon they started fighting each other, in the Wars of the Roses.