I just finished reading the new book about Mithradates by Adrienne Mayor. Mithradates was the king of ancient Pontus, in modern day Turkey on the Black Sea, at the end of the Roman republic. He fought against the expansion of the Romans for forty plus years. Even though he had successes, he could never defeat the Romans. They always had a new general and legions to throw against him. I think there are several reasons why the Romans could always defeat him, even when they were badly outnumbered.
- The Romans had a system that was independent of personalities. Mithradates ruled personally. He didn't hesitate even to kill his own children if he felt threatened by them.
- The Romans were united even when fighting. All the members of the Roman army spoke the same language and worked together. Mithridates armies were formed from people from many countries and cultures who must have had difficult communicating.
- Mithradates had bad luck. Many times he should have won, but fortune swung to the Romans. It even looked as though the gods were against him at times.