Mussolini wanted to bring back the good old days of the Roman Empire, and as you may recall, Rome had previously fought a lengthy series of wars with Carthage in northern Africa. By invading Ethiopia, Italy sought to recapture its lost glory.
Benito Mussolini claimed his unrelenting power by making the claim that Italy would gain back the glory of the magnificent Roman empire. Because the roman empire was the largest of its time, his claim also included the necessity of expansion.
After the fall of the Western Roman Empire, Emperor Justinian was able to bring back many traits and traditions of the Roman empire. Justinian not only was able to revive the Roman Empire, but was able to create his own legacy. (yes, I am in AP World History)
He did not conquer Greece. He attempted to bring the independent Greek city-states under control to bring peace and stop them disrupting his empire, but failed. The Greeks went back to fighting each other.