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 "They argue that Rome's expansion was driven by short-term defensive and inter-state factors (that is, relations with city-states and kingdoms outside Rome's hegemony), and the new contingencies that these decisions created.". Is that enough to answer the question?
Answer: yes