When Gascogne was linked once more to Aquitaine by the Treaty of Meaux in 1229, the county of Armagnac was the most powerful of the fiefs of Gascony.

During the Hundred Years' War the southern part of France, including Armagnac, was ceded to England by the Treaty of Brétigny (1360).

By submitting themselves to King Charles V of France, noble families like the Armagnacs were able to retain much of their former power and assure themselves of protection.

When Burgundy allied itself with England during the later stages of the Hundred Years' War, the friction between the two parties greatly increased.

After peace was established, many veterans originally recruited by Count Bernard VII formed mercenary bands that also became known as the Armagnacs.

After the death of Bernard VII in 1418, the counts of Armagnac gradually lost their powerful position in southern France.

However, King Francis I gave the district to a nephew of the last count, and it subsequently passed by marriage to the family of Henry of Navarre.

In 1645, Louis XIV granted the title to Henri de Lorraine-Harcourt, whose heirs possessed it until the Revolution.

During the 17th and 18th centuries, the County of Armagnac was an administrative division of the General Government of Guyenne and Gascony (Gouvernement-Général de Guienne et Gascogne).