Mussolini's rise to power was caused largely by political problems.
After World War I, Italian politics was in complete turmoil. It seemed to many Italians as if their parliamentary system had completely stopped working. They also blamed the parliamentary system for the fact that Italy did not get as much as it wanted in the way of territorial gains at the Paris peace conference.
The political turmoil was not the only factor that helped Mussolini come to power. There was also social turmoil as there were many strikes in factories as well as examples of peasants seizing land from large estates. These sorts of problems worried people as well and helped Mussolini seem like a good option.
All in all, then, political problems played a major role in bringing Mussolini to power, but social issues were important as well.