Most of the nobility supported Charles of Blois, so if John of Montfort was to have any chance, it was dependent upon swift action before organized resistance could be made. John quickly took possession of the
ducal capital
Nantes and then seized the Ducal treasury at
Limoges. By the middle of August, John of Montfort was in possession of most of the Duchy, the three principal cities of Nantes,
Rennes and
Vannes. Up to this point, the succession crisis had been a purely internal affair. But to complicate things further, the
Hundred Years' War between England and France had broken out four years earlier, in 1337. In 1341, there was a truce between the two countries, but there was little doubt that hostilities would be renewed when the truce ended in June 1342. Thus, when rumours reached
Philip VI of France that John of Montfort had received English agents, the French Crown naturally took a more direct interest in their small neighbors situation. Charles of Blois became the official French candidate. Whatever had been his original intentions, John of Montfort was now forced to support through force,
Edward III of England as King of France. Edward III was bound by the truce not to take any offensive action in France. Nothing in it, however, impeded France from subduing rebellious vassals. In November, after a short siege and defeat at the
Battle of Champtoceaux, John of Montfort was compelled to surrender at
Nantes by the citizens. He was offered safe conduct to negotiate a settlement with Charles of Blois, but when this led nowhere he was thrown in prison. It now fell upon John's wife,
Joan of Flanders, to lead the Montfortist cause. Deeming her possessions in the east indefensible, she set up headquarters at
Hennebont in western Brittany but was driven into Brest and besieged, the siege being broken by the arrival of an English army under the
Earl of Northampton at the
naval battle of Brest on 18 August 1342. Northampton then made his way inland and besieged Morlaix after an unsuccessful initial attack. The siege was lifted after the
battle of Morlaix on 30 September. In Paris it was feared that Edward III would land at
Calais once the truce ran out. The major part of the French army was therefore withdrawn, and Charles of Blois was left to pursue his claim on his own. Charles soon proved himself to be an able soldier: Rennes and Vannes were taken and many of the Montfortist captains defected. In late November,
Edward III arrived with his army at
Brest. He almost at once marched against Vannes.
The siege dragged on and a French army was assembled to meet him, but on 19 January 1343, before any major engagements could be fought, the two kings agreed the
Truce of Malestroit. Vannes was taken into papal custody. With John of Montfort in prison, his son an infant, and his wife recently gone mad, the places under Montfortist control were in practice administered from London, with a large permanent English garrison at Brest. The truce was to last until 29 September 1346 with the hopes that in the meantime the disputes between the two kingdoms could be permanently settled, but in Brittany it made little difference. The truce bound the two kings and their followers, but Charles of Blois claimed to be fighting his own separate war and was therefore not bound by any truce. The brutal small-scale fighting continued at the same pace. In Paris, John of Montfort was released from prison on 1 September 1343 in return for a huge bond and a promise to stay on his estates in the east. The English coastal garrisons held firm, but the Montfortist party continued to crumble. They had some successes, such as the expulsion of the papal custodians from Vannes, but with no unifying leadership, mostly they were reduced to pleading for men and money from London. To hamper communication between Brest and Vannes, Charles of Blois laid siege to
Quimper in early March 1344. The city fell by assault on 1 May and, as usual at that time, this meant the slaughter of civilians in huge numbers, estimated between 1,400 and 2,000. The English prisoners were held for ransom, but the Breton and Norman captives were dispatched to Paris where they were executed for treason. During the summer and autumn, the Montfortist party fell apart. Even those who had been John of Montfort's staunchest allies now considered it futile to continue the struggle. It, therefore, mattered little that in March 1345 John finally managed to escape to England. With no adherents of note of his own, he was now little more than a figurehead for English ambitions in Brittany. Edward III decided to repudiate the truce in summer 1345, a year before it was due to run out. As part of his larger strategy, a force was dispatched to Brittany under the joint leadership of the
Earl of Northampton and John of Montfort. Within a week of their landing in June, the English had their first victory when Sir
Thomas Dagworth, one of Northampton's lieutenants, raided central Brittany and defeated Charles of Blois at Cadoret near
Josselin. The follow-up was less impressive. Further operations were delayed until July when Montfort attempted the recapture of Quimper. However, news had reached the French government that Edward's main campaign had been canceled and they were able to send reinforcements from Normandy. With his strengthened army, Charles of Blois broke the siege. Routed, Montfort fled back to Hennebont where he fell ill and died on 16 September. The heir to the Montfortist cause was his five-year-old son,
John. During the winter, Northampton fought a long and hard campaign with the apparent objective of seizing a harbour on the north side of the peninsula. Edward III had probably planned to land here with his main force during summer 1346. However, the English achieved very little for their efforts. Northern Brittany was Joan of Penthièvre's home region and resistance there was stiff. In the end, Edward decided upon Normandy as the landing spot for his 1346 campaign. Northampton was recalled and Thomas Dagworth was appointed as deputy lieutenant. It was during a tour through the English strongholds on 9 June that Dagworth and his escort were trapped by Charles of Blois and his army near
Saint-Pol-de-Léon. They dug in on a hilltop and fought off all attacks until nightfall when Charles was forced to retreat leaving many of his wounded behind. ==Tide turns against Charles==