Explanation: In the Roman Empire, and especially in the later years of the Empire, the Praetorian Guard - nominally the bodyguard of the Emperors - had a nasty tendency of ‘interfering’ with political matters to their own benefit.

Funny enough, this is both exaggerated and downplayed by the meme. In the Year of the Five Emperors, only two of the Emperors were couped by the Praetorian Guard - Pertinax, for refusing to give the Praetorians a bigger bonus, and Didius Julianius, for being a loser. The other two failed Emperors were killed by the traditional method of bloody civil war.

Downplayed in that Didius Julianus, who quite literally bought the position of Emperor, actually offered each Praetorian over ten years’ pay as a bonus in exchange for handing him the Emperorship.