The Agen region occupied a sensitive frontal position. Its territories were disputed by local and international forces and changed hands eleven times between the end of the 12th century and 1370.

The Origins of the War
It all dates back to 1152, when the beautiful Eleanor of Aquitaine divorced the King of France to marry Henry Plantagenet, who was to become King of England. This meant that an English King was also the vassal of the King of France, (not the easiest of situations). And so for three centuries possession of Agen swung back and forth between the Duke of Aquitaine (King of England) and the King of France, with occasional ownership by the Count of Toulouse and even Simon de Montfort during his Crusade against the Albigensians. 
Friction between France and England began soon after Eleanor's marriage to Henry Plantagenet. By the mid 13th century, the Agen region was back under French control in the person of Philip the Hard,( Philip III). But as part of a political treaty, Philip handed Agen and its territories back to the Plantagenets at a grand ceremony held at the Jacobins Church in Agen in 1279. 
However, tensions continued and there were frequent border skirmishes. The Agen region found itself in the front line and the extra fortification of castles, towns and " Bastide " villages dates from this time. 
This was the background to an incident in 1323 at St. Sardos, (a " Bastide " village now in the Lot-et-Garonne), which was typical of the time, but which many credit with precipitating the Hundred Years' War. 
This was then English territory, but the village Priory belonged to the Abbey of Sarlat in Dordogne, which was loyal to the French King, Charles IV. Despite strong protests from the English, Charles founded a " Bastide " on the site. On the day of the official ceremony to mark this alliance, the neighbouring baron, Raymond-Bernard de Montpezat, backed up by English troops, attacked St.Sardos Castle and razed the village. The garrison was put to the sword and the King of France's representative hanged. 
Charles in revenge invaded the whole of Aquitaine. He was forced to hand it back, reluctantly, in 1325, but hostilities were only in abeyance.

The Official Declaration of War
On the death without succession of Charles the Handsome in 1328, the King of England, his nephew Edward III, had a strong claim to the throne of France. But Edward was passed over under Salic law in favour of Philip, Count of Valois, and so a dynastic element was added to the territorial quarrel. Edward paid hommage to Philip at Amiens in 1329, but this did not stop the French invading the Guyenne region once more in 1337. Edward broke off relations with Philip and the Hundred Years' War officially began. 
Local barons with no particular allegiance took advantage of the conflict and Agen had to defend itself against them.

 
In just one year, 1340, the Agen barons were sollicited in turn by Edward III and then by the future French King , John the Good, (at the time the King's Lieutenant in Languedoc), who received their allegiance at a ceremony in the Jacobins Church. It was John who evicted the Cordeliers from their monastery on the banks of the Garonne in order to create a fortification to dominate the Garonne valley. 
A period of English military dominance, marked by the Battle of Crécy in 1346, ensued, but the Black Death of 1348, which caused the death of 25 to 30 percent of the population of Europe, interrupted hostilities. 


War resumed in 1351 in the form of raids led by Edward, Prince of Wales, the Black Prince, into French territory and in 1356 the Black Prince defeated the French armies at Poitiers and captured the French King, John II, the Good. At the same time the privations of war and increased taxation led to popular uprisings in France.

The Height of English Domination
Peace negotiations with Edward III in 1360 led to a disastrous treaty for France, which saw a quarter of Philip the Handsome's territory, including the Aquitaine, ceded to the English. The Black Prince became Prince of Aquitaine and he was received in all pomp and ceremony at Agen in 1364. The Agen region once again became English. 
But popular discontent with English rule led to uprisings, which allowed the King of France to resume hostilities. By 1380, the English only retained Calais and the Bordeaux and Bayonne regions. 
However, the death of the French King led to a period of political instability, from which Henry V of England profited by regaining his lost territories and crushing the French nobility at Agincourt in 1415. 
Henry then married the daughter of Charles VI and his son was to inherit the French throne.

Reconquest
In 1429, the epic story of Joan of Arc introduced a revival of French patriotism and the reconquest of the old French territories. Pothon de Xantrailles, whose home estates were only 25 km from Agen, was one of Joan's most famous companions. It took nearly 20 more years for the whole of Aquitaine to succumb to French rule. The Agen/Guyenne region was retained by the English till the very last because of the quality of its wine. But by 1453, Agen and the Guyenne were once and for all part of the Kingdom of France.