Earlier quoted context omitted.
I'm afraid democracies are inherently unstable. Athenian lasted 200 years and got swallowed up by Macedonian autocracy. Roman lasted 500 years and got overthrown by the army. Polish lasted 350 years and the parliament voted to allow neighbouring empires to divide the country. The US is at 250 years and people are seriously worried about it devolving into either Gilead or Cyberpunk any moment now.
> Roman lasted 500 years and got overthrown by the army Byzantium (and the rest of the Eastern Roman Empire) disagrees [0]. They lasted until 1453 - incidentally only 50 years before Columbus sailed. [0] https://en.wikipedia.org/wiki/Byzantine_Empire
Sidenote: incidentally not coincidentally. The closure of the Silk Road and other important East-West land routes as a result of the Ottoman conquest was one of the important spurs that kicked off the Age of Discovery, as everyone scrambled to find new routes.