How did the ancient Romans create a huge and long-lasting empire, when the ancient Greeks were never able to unify for very long?

The most
important factor was geography. Greece is extremely mountainous, making land travel between
different regions quite difficult. Although Greece had been inhabited in the neolithic age,
Greek culture as we think of it began in a period know as Early Helladic III, starting in
roughly 2200 BC as Greek-speaking peoples gradually moved into the area that became Greece.
These Bronze Age towns grew in a pattern that was determined by geography. Usually there was an
urban center, often a fortified...