Great as was Henry's authority many of the princes, chief among them being Adolph, archbishop of Cologne (d. 1220), refused to recognize his son, Frederick, who had been chosen king of the Romans in 1196. This attitude was possibly owing to the fact that Frederick was young and inexperienced; it was, however, more probably due to a revival of the fear that the German princes would be entangled in Italian politics. For a time Adolph and his friends, who were mainly princes of the Rhineland, sought in vain for a new king. While they were thus employed the friends of the house of Hohenstaufen, convinced that Frederick's kingship was not possible, chose the late emperor's brother, Philip, duke of Swabia, to fill the vacant throne; soon afterwards the enemies of the house found a candidate in the person of Henry the Lion's son, Otto of Brunswick, who was also chosen German king. Thus the struggle between Welf and Hohenstaufen was renewed and civil war broke out at once. Philip's supporters were the nobles of southern and eastern Germany, while a few cities in the west owned his authority; Otto's friends were found mainly in the north and the north-west of the country. The number of available warriors was increased by the return of many crusaders, among them being the famous soldier, Henry von Kalden, who was mainly responsible for the success of Philip's cause in 1199. If Germany had been unconnected with the Papacy, or even if the Papacy had been as weak as in the days of Henry VI., the issue of the strife would almost certainly have been an early victory for Philip. A majority of the princes were on his side and the French king Philip Augustus was his ally, while his personal character commanded general respect. Otto, whose chief supporter outside Germany was his uncle Richard I. of England, on the other hand was a harsh and violent man. But unfortunately for Germany the papal chair at this time was occupied by Innocent III., a pope who emulated Hildebrand in ambition and in statesmanship. At first vacillating, but by no means indifferent, Innocent was spurred to action when a number of princes met at Spires in May 1200, declared Philip to be the lawful king, and denied the right of the pope to interfere. He was also annoyed by Philip's attitude with regard to a vacancy in the archbishopric of Cologne, and in March 1201 he declared definitely for Otto. The efforts of the pope helped to rekindle the expiring flames of war, and for a year or two success completely deserted Philip. He lost the support of Ottakar of Bohemia and of Hermann I., landgrave of Thuringia; he was driven from North Germany into Swabia and Otto's triumph seemed assured. From 1204 onwards, however, fortune again veered round, and Philip's prospects began to improve. Deserted by Ottakar and even by Adolph of Cologne and his own brother Henry, count palatine of the Rhine, Otto was forced to take refuge in Brunswick, his last line of defence, and was only saved by Philip's murder, which occurred at Bamberg in June 1208. A feature of this struggle was the reckless way in which the rival kings gave away the property of the crown in order to gain adherents, thus enriching the princes and weakening the central government.