I. Edward III's War
1337-43: The French try to strip Edward III of his fiefs south of the Loire. This is the immediate cause of the war, as Edward objects. The English resist and send raiding parties into Northern France and Flanders.
1338: Edward III declared himself King of France (via his mother, a daughter of Philip IV). Holy Roman Emperor supports Edward.
1340: British fleet (150 ships ) destroys or captures 166 of 190 French ships at Sluys: Present at the battle is a young lad of 12 or so, the future "Black Prince" and his 10-year old brother, John of Gaunt. The English more or less dominate at seas for the rest of the war.
1341-43: Civil War in Brittany. Philip VI supports Charles of Blois, Edward supports John de Montfort.
1346: Crecy. French invade Gascony, English send 20,000 man army (3,000 men at arms, 3,000 squires and light cavalry, 10,000 English archers, 2,000 Welsh archers and 2,000 Welsh light infantry). English troops were professionals, raised under indenture system whereby King paid Barons to maintain troops (who nevertheless owed allegiance to King). There was still a feudal levy, but was not called out unless England was threatened. Indenture troops were basically mercenaries, and ill paid most of the time. They were prone to unruliness, which was never a big problem as they could be allowed to rampage over the French countryside, using English Kings French fiefs as bases. These troops were the best in Europe, indeed were probably the best seen since the demise of the Roman legions. These troops could all ride, but generally preferred to fight on foot. They were thus mobile, and formidable against any feudal host. The French brought up 60,000 troops (12,000 men at arms, 17,000 squires (etc), 6,000 Genoese crossbowmen, and 25,000 of the feudal (untrained light infantry)). French lost 15,000 dead, including 1,500 nobles. English had 200 dead and wounded. This was one of the first major victories of infantry against a major feudal host.
1347: English lay siege to Calais for a year and capture it.
1347-1354: Black Death broke out and halted operations.
These opening stages of the war revealed patterns of loyalty and betrayal that were to characterize the entire war. For example, the Comte de Foix was a strong ally of the Black Prince in most, if not all, of his predations through southern France. Lord Douglas was a Scot who fought on the French side, and was present at Crecy and Poitiers, where he died. The House of Navarra was usually, but not always, an ally of England. The Duchies of Brittany and Normandy were usually on the English side as well. In Brittany, there was a civil war fought over the succession, and the English-bscked contender won.