27 BCE (Fall of the Republic)

395 AD (Split of the Empire into East and West)

476 AD (Fall of the city of Rome and the Western Empire)

717 AD and 867 AD (Byzie stuff? Not sure)

1204 AD (Sack of Constantinople and the break of government continuity in the Byzantine Empire)

1453 AD (Siege of Constantinople and conquest of the Byzantine Empire by the Ottoman Turks)

1806 AD (Dissolution of the Holy Roman Empire, the Germanic state which claimed legitimacy by being crowned by the Pope)

1917 AD (Fall of the Romanov dynasty which claimed dynastic continuity with the Byzantine Empire and called Russia the ‘Third Rome’)