Rough Roman Memes

Oh, yes, you are absolutely correct there! Like I said - there were a great many causes for the Republic's level of... enthusiastic expansion. We could go into the fact that the entire Roman state was organized around war, or the cultural value placed by Romans on their own superiority, or the relative equality of citizenry in the state, or the Republic's willingness to include outsiders to a place within the polity (and not just under it); but the full list of reasons takes up entire books and libraries.

At the same time, you can see a distinct difference in the consistency of aggressive policy between city-state style polities, like Rome and most pre-Alexander Greek city-states, which cultivated intense bonds between their citizenry and the very abstract state they belonged to; and traditional kingdoms and broader confederations, whose aggression waxed and waned with their leadership's decisions.