They spent a significant proportion of the 600 years between ~100BC and 500 AD fighting pointless and often very brutal civil wars.

~3/4ths or all Roman emperors died by various violent means. The Romans spent unsustainable amounts of money (resulting in veryhigh levels of taxation) to fund a massive army often the main purpose of which was fighting other Romans. Until it was too late... by the end not that many actual Romans were even willing to fight and die to save the empire.

Sure it's spectacular that they not only managed to survive but often even thrive despite that, still. Not sure if its the best example to follow.