When the conflict broke out, France, more populous and richer (15 million inhabitants against 4 for England proper), seemed likely to easily triumph over England. But if the latter, by its economy of semi-colonial character as by its cultural development, is experiencing a certain delay, on the other hand its administrative and governmental structures rank among the most advanced. These assets will prove decisive in the first phase of the conflict against an adversary who is going through a serious economic and financial crisis.
The first English rides in the north of France are without results but important diplomatic successes come to compensate for them. Edward III skilfully plays on the economic interests that bind Flanders to England to detach the Netherlands from the French orbit:by prohibiting the export of English wool essential to the Flemish cloth industry, he provokes and encourages the revolt of the rich Flemish cities, behind - Jacques van Artevelde, against their count, Louis de Nevers, who remained faithful to Philip VI, and signed a treaty with them by which they undertook to help him militarily and to accept him as true king of France (1339). He also supported Robert d'Artois in revolt against Philippe VI, won Hainaut and Brabant to his cause by transferring part of the English interests to these regions, and contracted numerous alliances in Germany. Much better:during the summer of 1337, he allied himself with the Emperor Louis IV, who the following year appointed him his imperial vicar for the left bank of the Rhine.
By this coalition, the French monarchy found itself threatened from two sides at once. On the strength of these successes, Edward III solemnly assumed in Ghent, in January 1340, the title of King of France, introducing the fleur-de-lys into his Great Seal and into his coat of arms. Five months later, on June 24, 1340, the French fleet was completely defeated at L'Écluse, near the outer port of Bruges. Disaster which caused France to lose control of the sea. The conflict rebounded with the beginnings of the War of the Succession of Brittany which opposed two candidates, Jean de Montfort, supported by Edward III, and Charles de Blois supported by Philippe VI. A truce interrupted him in January 1343. Edward III could then resume his other plans. A new English army, landed in Normandy, engages in the first of the great English rides. After traveling more than 350 kilometers in a month, she met the French army at Crécy on August 26, 1346. Again, the French defeat was complete. Resuming his journey, Edward III arrives under the walls of Calais. After an eleven-month siege (September 1346-August 1347), the city had to surrender (episode of the six bourgeois of Calais). Having become English, it will succeed Bruges as the main place for English merchants. Following these successive failures, the position and authority of Philip VI inevitably deteriorated, and the French monarchy went through a serious internal crisis, marked by a veritable palace revolution around the king. However, neither Crécy nor Calais definitively settled the Franco-English dispute, and a truce was concluded on September 28, 1347. It was extended until June 1355 by an event external to the conflict:the Black Death which, coming from Asia, spread to France and England in 1347.
When Philip VI died in 1350, the balance sheet of his reign was far from positive. The only favorable element, the new Count of Flanders, Louis de Male, taken prisoner at Crécy, was able to escape and in 1349 obtain the submission of the Flemish cities. Reversal of the situation which results for Edward III in the loss of a precious support. He was never to find him. On the other hand, in the first years of the reign of the new king of France, Jean le Bon, he obtained another major ally:Charles the Bad, king of Navarre, who, annoyed at not obtaining any territorial compensation for the price of his abandonment of the county of Angoulême in favor of the crown, openly revolts against the king. He agrees to submit after having received the county of Beaumont-le-Roger and most of Cotentin, but this reconciliation has no future. It will be followed by twenty-five years of plots and intrigues. On the same date, the failure of new Franco-British negotiations drove Jean le Bon to war.
The campaign of 1355-1356 was led, on the English side, by the eldest son of Edward III, the Black Prince, who, after leading a successful ride through Languedoc in 1355, inflicted on Jean le Bon the heavy defeat of Poitiers (September 19, 1356). The King of France is among the prisoners. News of the disaster was followed by an outbreak of revolt against royal authority. Dauphin Charles, then 18 years old, had to face organized opposition, led by Robert Le Coq, bishop of Laon, who had become the minion of the king of Navarre, and especially Étienne Marcel, provost of the merchants of Paris. The design of the latter is to undertake, according to the word of the time, the reform of the State, to remove its most corrupt personnel and to establish over the monarchy a control exercised by representatives of the three orders by means of 'a council which would have the power to do everything and order the kingdom as well as the king'. The Dauphin had to give in and ratify the Grand Ordinance of March 1357. But, while the Estates General, expressing above all the views of the Parisian bourgeoisie, formulated ever greater demands, the more moderate Provincial Estates sought above all to control the collection and use of taxes, without worrying too much about the great politics that they willingly abandoned to royal power. Soon the situation turns to the disadvantage of Étienne Marcel who can only count on the capital. A new danger appears with the peasant uprising of the Jacques, an insurrection of misery, directed against the privileged. He is quickly crushed. Étienne Marcel loses all his popularity when his collusion with the English becomes evident. He was assassinated in 1358, and the Dauphin was able to enter Paris. The Parisian revolution failed. It is the triumph of the monarchy. Once order is restored, negotiations can begin with the English, all the more the game. They lead to the hard treaty of Brétigny, signed on May 1, 1360. Edward III receives in all sovereignty a large Aquitaine, going from the Loire to the Massif central and the Pyrenees, Calais and its steps, Ponthieu and the county of Guines:the third of the kingdom approximately. Jean le Bon's ransom is set at 3 million crowns. On the other hand, Edward III renounces the crown of France and undertakes to abandon the fortresses occupied by his troops in the part of the kingdom remaining to the Valois. We can think of a lasting pacification of the West.