It was not to be supposed that Frederick would ever forgive that act of Henry the Lion by which the whole aspect of the war in Italy had been changed.  Yet it is probable that technically Henry had committed no offence against the Empire; for no charge of desertion or “herisliz,” as refusal to do military service was called, or even of neglect of feudal duties, was ever brought against him.  He probably possessed some privilege, like that bestowed on Henry Jasomirgott, rendering it optional with him to accompany the Emperor on expeditions out of Germany.

But the circumstances had been so exceptional, so much had hung in the balance at the time of Frederick’s appeal for aid, that no one can blame the Emperor for now letting Henry feel the full weight of his displeasure.  Nor was an occasion lacking by which his ruin might be accomplished.  For years the Saxon nobles and bishops had writhed under Henry’s oppressions, and the Emperor had hitherto taken sides with his powerful cousin; he now lent a willing ear to the charges of the latter’s enemies.

The restitution to Udalrich of Halberstadt of his bishopric, a restitution that had been provided for in the treaty of Venice, gave the signal for the conflict.  Henry the Lion refused to restore certain fiefs which, as Udalrich asserted, belonged to the Halberstadt Church.  Archbishop Philip of Cologne and others came forward with similar claims.

Henry was repeatedly summoned to answer his accusers, but did not deign to appear.  On the contrary he prepared to raise up for himself allies and to besiege the castles of those who would not join him.  His own lands were thereupon laid waste by his private enemies, and that with the Emperor’s consent.  But Halberstadt, which took part in one of these plundering expeditions, suffered a terrible vengeance at the hand of the enraged Guelf.  In one destructive blaze the city, churches and all, was reduced to ashes.  In the war that he was now waging Henry did not hesitate to call in even the Wends to his aid, but Westphalia was soon lost to him, and only in East Saxony was he able to maintain himself.

At a diet held in Wuerzburg in January, 1180, the Emperor laid the question before the princes what was to be done to one who had refused, after having been three times summoned, to come before the imperial tribunal.  The answer was that he was to be deprived of all honor, to be judged in the public ban, and to lose his duchy and all his benefices.  Thus was final sentence passed on the chief man in Germany next to the Emperor himself.

An imperial army was now raised and several fortresses were besieged.  No battle took place, but the fact that Frederick had a large force at his command was sufficient to cause defection in the ranks of Henry’s allies.  In 1181 the Emperor’s army marched as far as Lubeck, which city, Henry’s proudest foundation, was forced to submit.  The whole region north of the Elbe followed Lubeck’s example, and Henry was soon forced to confess that his cause was hopeless.  He laid down his arms, and was summoned to a diet at Erfurt to learn his fate.  Here he fell on his knees before Frederick, who, with tears in his eyes, raised him and kissed him in token of peace.