The Hundred Years' War (French: Guerre de Cent Ans) is a prolonged conflict between two royal houses for the French throne, vacant with the extinction of the senior Capetian line of French kings.

The two primary contenders are the House of Valois, and the House of Plantagenet.

The House of Valois claims the title of King of France, while the Plantagenets from England claim to be Kings of France and England.

The Plantagenet Kings in England, also known as the House of Anjou, have their roots in the French regions of Anjou and Normandy.

French soldiers fight on both sides, with Burgundy and Aquitaine providing notable support for the Plantagenet side.The conflict lasts one hundred and sixteen years from 1337 to 1453.

The war is punctuated by several brief periods of peace, and two lengthy periods of peace, before it finally ends in the expulsion of the Plantagenets from France (except the Calais Pale).

Subtracting the two long periods of peace from 1360–69 and 1389–1415, the war is fought for about eighty-one years.The war is in fact a series of conflicts and is commonly divided into three or four phases: the Edwardian War (1337–1360), the Caroline War (1369–1389), the Lancastrian War (1415–1429), and the slow decline of English fortunes after the appearance of Joan of Arc (1412–1431).

Several other contemporary European conflicts are directly related to the conflict between England and France: the Breton War of Succession, the Castilian Civil War, and the War of the Two Peters.

The term "Hundred Years' War" is a later term invented by historians to describe the series of events.The war owes its historical significance to a number of factors.

Though primarily a dynastic conflict, the war gives impetus to ideas of both French and English nationality.

Militarily, it sees the introduction of new weapons and tactics, which erode the older system of feudal armies dominated by heavy cavalry.

The first standing armies in Western Europe since the time of the Western Roman Empire are introduced for the war, thus changing the role of the peasantry.

For all this, as well as for its long duration, it is often viewed as one of the most significant conflicts in the history of medieval warfare.

In France, the English invasion, civil wars, deadly epidemics, famines and marauding mercenary armies turned to banditry reduce the population by two-thirds.

When the war begins, France has a population of about 17 million, whereas England has about 4 million.

Moreover, France is generally considered to have the most knights in Europe.Open hostilities break out as French ships began scouting coastal settlements on the English Channel and in 1337 Philip reclaimed the Gascon fief, citing feudal law and saying that Edward has broken his oath (a felony) by not attending to the needs and demands of his lord.

Edward III responds by saying he is in fact the rightful heir to the French throne, and on All Saints' Day, Henry Burghersh, Bishop of Lincoln, arrives in Paris with the defiance of the king of England.

War has been declared.