It was not till the next year but one that Henry renewed his invasion of France--the intervening space was spent in negotiations with Burgundy, and with the emperor Sigismund, whose aid the king secured in return for help in putting an end to the scandalous "great schism" which had been rending the Western Church for so many years. The English deputation lent their aid to Sigismund at the council of Constance, when Christendom was at last reunited under a single head, though all the reforms which were to have accompanied the reunion were postponed, and ultimately avoided altogether, by the restored papacy.
In July 1417 Henry began his second invasion of France, and landed at the mouth of the Seine with a powerful army of 17,000 men. He had resolved to adopt a plan of campaign very different from those which Edward III. or the Black Prince had been wont to pursue, having in view nothing more than the steady and gradual conquest of the province of Normandy. This he was able to accomplish without any interference from the government at Paris, for the constable Armagnac, who had succeeded the captive Orleans at the head of the anti-Burgundian party, had no troops to spare. He was engaged in a separate campaign with Henry's ally John the Fearless, and left Normandy to shift for itself. One after another all the towns of the duchy were reduced, save Rouen, the siege of which, as the hardest task, King Henry postponed till the rest of the countryside was in his hands. He sat down to besiege it in 1418, and was detained before its walls for many months, for the citizens made an admirable defence. Meanwhile a change had taken place in the domestic politics of France; the Burgundians seized Paris in May 1418; the constable Armagnac and many of his partisans were massacred, and John the Fearless got possession of the person of the mad Charles VI., and became the responsible ruler of France. He had then to choose between buying off his English allies by great concessions, or taking up the position of champion of French interests. He selected the latter rôle, broke with Henry, and tried to relieve Rouen. But all his efforts were foiled, and the Norman capital surrendered, completely starved out, on the 19th of January 1419. On this Burgundy resolved to open negotiations with Henry; he wished to free his hands for an attack on his domestic enemies, who had rallied beyond the Loire under the leadership of the dauphin Charles--from whom the party, previously known first as Orleanists and then as Armagnacs, gets for the future the name of the "Dauphinois." The English king, however, seeing the manifest advantage of his position, tried to drive too hard a bargain; he demanded the old boundaries of 1360, with his new conquest of Normandy, the hand of the princess Catherine, and a great sum of ready money. Burgundy dared not concede so much, under pain of alienating all his more patriotic supporters. He broke off the conference of Meulan, and tried to patch up a peace with the dauphin, in order to unite all Frenchmen against the foreign invader. This laudable intention was wrecked by the treachery of the young heir to the French throne; on the bridge of Montereau Charles deliberately murdered the suppliant duke, as he knelt to do homage, thinking thereby that he would make an end of the Burgundian party (Sept. 9, 1419).