The accession of Dayarvesh (Darius) in what we would today call a coup is documented in both Persian (the famous Behustan Rock!) and Greek (Herodotus) sources. Herodotus reports a debate between Dayarvesh and his fellow coup plotters; Otanes argued for democracy, Megabyzus for oligarchy, and Darius for monarchy. Darius won the argument and Persia would remain an absolute monarchy until its overthrow by the Muslim Arabs over 1,100 years alter.
Bavli Avodah Zara 10a points out that the Roman Empire didn’t have monarchs in the usual sense of the term, in that it was not hereditary. (Secular sources point out that Rome maintained most of its republican instittuions until the late 3rd century CE, and at least in theory the Emperor was subject to the law not above the law.) Emperors would typically designate a successor and in Avodah Zara 10a-b Rebbe tells Antoninus that it is okay that it be his biological son, which was quite rare until that point. If Antoninus was the Emperor better known as Marcus Aurelius, then Rebbe’s advice triggered the decline and fall of the Roman Empire because Marcus Aurelius’s son Commodus turned out to be a disaster, leading a venal and corrupt administration and promoting a personality cult of himself before being assassinated. Rome never fully recovered.