The collapse of the Roman Republic might be more relevant to current events than the empire.
https://www.amazon.com/Mortal-Republic-Rome-Fell-Tyranny/dp/0465093817
Interview with the author here:
For 300 years, this system worked quite well in Rome, but for the past century or so of its existence these tools of deliberation were used not to facilitate compromise but to obstruct and punish political enemies and basically prevent anything from happening. That destroyed the goodwill within the system and really poisoned it in the minds of the voters
This book is short, quick read:
This one was very good.