Stephen Kostromanić was succeeded by his young nephew, Stephen Tvrtko, under the regency of his mother, Helena. Under such circumstances, dissatisfied and insubordinate Catharan magnates had ample opportunity to produce confusion. Of this full advantage was taken by Louis of Hungary as soon as the death of Dusan the Great, in 1355, relieved him from that formidable antagonist. The Dominicans hastened, in 1356, to obtain from Innocent VI. a confirmation of the letters of John XXII., of 1327, authorizing them to preach a crusade against the heretics with Holy Land indulgences. Louis seized Herzegovina as a dower for his wife Elisabeth, reduced Stephen Tvrtko to the position of a vassal, and forced him to swear to extirpate the Cathari. Not content with this he proceeded to stir up rebellion among the magnates, producing great confusion, during which the Cathari regained their position. Then, in 1360, Innocent VI. conferred on Peter, Bishop of Bosnia, full powers as papal inquisitor, and also ordered a new crusade, which served as a pretext to Louis for a fresh invasion. Nothing was accomplished by this; but in 1365 the Cathari, irritated at Tvrtko’s efforts to suppress them, drove him and his mother from Bosnia. Louis furnished him with troops, and asked Urban V. to send two thousand Franciscans to convert the heretics. After a desperate struggle Tvrtko regained the throne. His brother, Stephen Vuk, who had aided the rebels, fled to Ragusa and embraced Catholicism, after which, in 1368, he appealed for aid to Urban V., representing that his heretic brother had disinherited him on account of his persecuting heretics. Urban accordingly urged Louis to protect the orthodox Vuk, and to force Tvrtko to abandon his errors, but nothing came of it. Whether Tvrtko was Catharan or Catholic does not clearly appear. Probably he was indifferent to all but his personal interests, and was ready to follow whatever policy promised to serve his ambition, and his success shows that he must have had the support of his subjects, who were nearly all Cathari. Although, in 1368, Urban V. congratulated Louis of Hungary on the success of his arms, aided by the friars, in bringing into the fold many thousand heretics and schismatics, Louis himself, in 1372, reported that Christianity was established in but few places; in some the two faiths were commingled, but for the most part all the inhabitants were Cathari. It was in vain that Gregory XI. endeavored to found Franciscan houses as missionary centres; the Bosnians would not be weaned from their creed. Had Tvrtko followed a policy of persecution he could not have accomplished the conquests which, for a brief period, shed lustre on the Bosnian name. He extended his sway over a large part of Servia and over Croatia and Dalmatia, and when, in 1376, he assumed the title of king, there was no one to dispute it. After his death, in 1391, the magnates asserted virtual independence under a succession of royal puppets--Stephen