Republican Rome was never conquered. Rome was sacked--which, it is often theorized, created a long-standing cultural fear of the Gauls/Celts that remained large

Republican Rome was never conquered. Rome was sacked--which, it is often theorized, created a long-standing cultural fear of the Gauls/Celts that remained largely until Julius Caesar's Gallic conquests/genocides--but the attackers did not stay and did not attempt to replace the governing apparatus. Roman history, particularly pre-imperial, does show a lot of "why exactly will they not just die?", but some level of resilience in large Mediterranean powers of antiquity was pretty common. (Carthage took two wars and decades to lose the Punic Wars.)