Henry did not cross the Channel again in the year 1416, which he spent partly in negotiations with the Duke of Burgundy, whose help he wished to secure against the Armagnacs, partly in treating with the Emperor Sigismund about the common welfare of Christendom. Sigismund was hard at work endeavouring to put an end to the "Great Schism," the scandalous breach in the unity of the Church caused by the misconduct of the rival Popes at Rome and Avignon. He visited England, and won Henry's aid for his plans, which brought about the reunion of Christendom at the Council of Constance--a reunion under evil auspices, since it was marked by the burning of the great Bohemian teacher John Huss, who had made the doctrines of Wicliffe popular among his Slavonic countrymen in the far East. Moreover, it restored the unity of Christendom, but did not reform either the papacy or the national Churches. As this was not done, the general outbreak of religious ferment was made inevitable in a later generation; after the failure at Constance to reform the Church from within, it became necessary to reform her from without. [Sidenote: =Second invasion of France.--Conquest of Normandy.=] Having come to an agreement with the Duke of Burgundy, and obtained from him a promise of neutrality, Henry invaded France for the second time in the summer of 1417. He took with him an army of somewhat over 16,000 men, landed in Normandy, and began to reduce one after another all the fortresses of that province. Utterly humbled by the memory of Agincourt, the Armagnacs made no attempt to meet him in the open field. Some of the Norman towns held out gallantly enough, but they got no aid from without. At the end of a year the whole duchy, save its capital, the city of Rouen, was in English hands. Henry then assumed the state of Duke of Normandy, and put the whole land under orderly government, a boon it had not enjoyed for twenty years. He gave Norman baronies and earldoms to many of his English followers, and handed over the control of the cities to burghers of the Burgundian faction, who served the English readily enough, out of their hatred for the Armagnacs. For thirty years Normandy was to remain English. Rouen was added to the rest of the duchy after a long siege of six months, in which half the population perished by hunger. Irritated by this long resistance, Henry imposed on it the harsh terms of a ransom of 300,000 crowns, and hung Alain Blanchart, the citizen who had been the soul of the obstinate defence (January, 1419). While the conquest of Normandy was in progress, the French factions had been more bitterly at strife than ever. In 1418 the Burgundian party in Paris rose against their rivals, and massacred every man on whom they could lay hands, including Bernard of Armagnac himself. The control of the party of the feudal noblesse then passed into the hands of the young dauphin Charles, the heir of France. [Sidenote: =Murder of the Duke of Burgundy.=]