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.