I want to know the answer to the following question:
What factor is considered by some to be the main driving force behind the expansion of Rome?
All the background I'm provided with is that "As such, early republican Rome was not an "empire" or "state" in the modern sense, but an alliance of independent city-states (similar to the Greek hegemonies of the same period) with varying degrees of genuine independence (which itself changed over time) engaged in an alliance of mutual self-protection, but led by Rome.". Is that enough to answer the question?
Answer: no