Fredericks attempt to conquer northern Italy led to severe problems.
The pope opposed him, fearing that he wanted to include Rome and the Papal States as part of his empire.
The cities of northern Italy, which had become used to their freedom, were unwilling to become his subjects.
An alliance of these northern Italian cities and the pope defeated the forces of Frederick I in 1176.
The main goal of Frederick II was to establish a strong, centrs
He too was involved in a struggle with the popes and the northern Italian cities.
Frederick waged a bitter struggle in northern Italy, winning many battles but ultimately losing the war.