Feudalism took hold in France during the 10th and 11th centuries, and Nantes was the seat of a county founded in the ninth century. Until the beginning of the 13th century, it was the subject of succession crises which saw the town pass several times from the Dukes of Brittany to the counts of Anjou (of the House of Plantagenet). During the 14th century, Brittany experienced a war of succession which ended with the accession of the House of Montfort to the ducal throne. The Montforts, seeking emancipation from the suzerainty of the French kings, reinforced Breton institutions. They chose Nantes, the largest town in Brittany (with a population of over 10,000), as their main residence and made it the home of their council, their treasury and their chancery. Port traffic, insignificant during the Middle Ages, became the city's main activity. Nantes began to trade with foreign countries, exporting salt from Bourgneuf, wine, fabrics and hemp (usually to the British Isles). The 15th century is considered Nantes' first golden age. The reign of Francis II saw many improvements to a city in dire need of repair after the wars of succession and a series of storms and fires between 1387 and 1415. Many buildings were built or rebuilt (including the cathedral and the castle), and the University of Nantes, the first in Brittany, was founded in 1460.