Polybius

Main point is that after 250 years the Roman Republic's constitutional balance of powers enabled the popular sustained effort and focus on long-term self interest through the first two Punic Wars. This was the birth of empire on an unprecendented scale.

Interesting to consider that the third Punic war, the preemptive destruction of Carthage, presaged the era of domestic military political violence that resulted in tyranny a mere century hence.