The real problem is that a Republic is an excellent system of government for a people who have a common set of values and identity, but it doesn’t work for running a far-flung empire.
A Republic needs *citizens* who value individual freedom and accept personal responsibility, trusting the government little and those who run it hardly at all.
An empire needs obedient subjects who fit into their place in a giant machine run by those who know best for them; there’s no other way to integrate people from many different cultures, with many different values and languages.
Rome after the second Punic war, as with the United States after WW2, gained an empire but lost a republic.
My thinking is the benefits of breaking the unwritten rules to gain power went up exponentially when the Republic because a de facto empire. It went from being number 1 in a city-state to being number 1 in an far flung empire.