Read John Adams.
Aristocracy (rule by the best few) descends into oligarchy (rule by the worst few).
And from oligarchy comes dictarship.
A classic example is the end of the Roman Republic.
The Annals of Tacitus
Augustus won over the soldiers with gifts, the populace with cheap corn, and all men with the sweets of repose, and so grew greater by degrees, while he concentrated in himself the functions of the Senate, the magistrates, and the laws. He was wholly unopposed, for the boldest spirits had fallen in battle, or in the proscription, while the remaining nobles, the readier they were to be slaves, were raised the higher by wealth and promotion, so that, aggrandised by revolution, they preferred the safety of the present to the dangerous past. Nor did the provinces dislike that condition of affairs, for they distrusted the government of the Senate and the people, because of the rivalries between the leading men and the rapacity of the officials, while the protection of the laws was unavailing, as they were continually deranged by violence, intrigue, and finally by corruption.