[Sidenote: Government of St. Engelbert, 1220–1225.] The long civil war between Frederick and Otto of Saxony had done much to shake the authority of the German king and stimulate the development of the feudal principle. A partial recovery was effected during the years succeeding the collapse of the Guelf, when the wise rule of Engelbert, archbishop of Cologne, contributed powerfully towards restoring the prestige of the absentee sovereign. Like Barbarossa, Frederick sought to rule by means of the German episcopate, but the bishops of his time were no longer in the commanding position which the warlike prelates of the twelfth century had held. The episcopal towns which they had once ruled through their officials had become great centres of commerce and wealth, and were rapidly advancing on the road to autonomy. The lay princes were more independent, and even the _ministeriales_, who had played so decisive a part in earlier struggles, were attaining an independent and permanent position of their own as a lower aristocracy whose imperial offices were becoming hereditary fiefs. There was not time enough for Engelbert’s attempts at reformation to succeed. It was not until 1219 that the last partisans of the Guelfs tendered their submission. But even before that, in 1216, Frederick had conferred on his four-year-old son Henry the duchy of Swabia, and in 1220 he had procured, as we have seen, his election as King of the Romans. He smoothed the way to this by a formal alliance with the ecclesiastical princes, conferring upon them a series of privileges that extended to them complete jurisdiction over their fiefs.[29] In 1222 Henry was crowned king at Aachen by Engelbert, who ‘cherished him as a son and honoured him as a master.’ Henceforth the administration was carried on in the name of the young king. Engelbert watched with a jealous eye the power of Valdemar II. of Denmark, who had been allowed by Frederick to retain possession of Nordalbingia and the extensive German districts which he had occupied, when fighting as a partisan of Otto IV. But the German lords of the conquered districts were averse to foreign domination, and, headed by Count Henry of Schwerin, sought to restore their estates to their fatherland. [Sidenote: Defeat of Valdemar of Denmark, 1223–1227.] In 1223 Henry of Schwerin had the good luck to take the King of Denmark prisoner, and in 1225 Valdemar only obtained his release at the price of renouncing Schwerin, Holstein, and his other German acquisitions. Afterwards Valdemar sought to regain his losses, but in 1227 he was defeated at the bloody battle of Bernhöved in Holstein, and was glad to renew the conditions which he had accepted two years before. Henceforth the Danes were confined to their own territories, and the chief hindrance was removed to the expansion of the German power in the Baltic lands.