The tensions between the Houses of Plantagenet and Capet climaxed during the so-called Hundred Years' War (actually several distinct wars over the period 1337 to 1453) when the Plantagenets claimed the throne of France from the Valois. This was also the time of the Black Death, as well as several civil wars. The French population suffered much from these wars. In 1420, by the Treaty of Troyes Henry V was made heir to Charles VI. Henry V failed to outlive Charles so it was Henry VI of England and France who consolidated the Dual-Monarchy of England and France.

It has been argued that the difficult conditions the French population suffered during the Hundred Years' War awakened French nationalism, a nationalism represented by Joan of Arc (1412–1431). Although this is debatable, the Hundred Years' War is remembered more as a Franco-English war than as a succession of feudal struggles. During this war, France evolved politically and militarily.

Although a Franco-Scottish army was successful at the Battle of Baugé (1421), the humiliating defeats of Poitiers (1356) and Agincourt (1415) forced the French nobility to realise they could not stand just as armoured knights without an organised army. Charles VII (reigned 1422–61) established the first French standing army, the Compagnies d'ordonnance, and defeated the Plantagenets once at Patay (1429) and again, using cannons, at Formigny (1450). The Battle of Castillon (1453) was the last engagement of this war; Calais and the Channel Islands remained ruled by the Plantagenets.