rome wound up with emperors as the end state of a long period of recurrent civil war that started over whether to allow italians to be roman citizens.
this prominently included the largely latin-speaking ‘socii,’ who were the same damn ethnicity as the romans by modern standards, but they weren’t roman. also other kinds of italians including traditional enemies now subjugated. whole-ass civil war about their being sub-citizen inhabitants of the republican empire.
they got citizenship and later (after more civil war) even the vote, but the republic never recovered from the destabilization and in a couple generations tipped over into a standing dictatorship, where the vote no longer counted for as much; eventually, for nothing at all.
but there was a path to citizenship for any free man, through the army.
septimius severus was however born a citizen, in an equestrian family. through his mother, he was descended from a respectable italian line who’d moved to the libyan colony and intermarried with locals, but his father was entirely provincial. his uncle got the emperor to promote him to senatorial rank to help him run for office.
(wikipedia says he probably started out getting elected to overseer of road crews, and that he was DA at one point. also it’s his wife that was syrian.)
he happened to be in command of an army nearby, having been elected to the tier of public service where they gave you armies because that was how it still worked at that point, when commodus was assassinated. (the historical event gestured toward by the movie gladiator.)
the replacement for commodus got assassinated even harder, and severus’ troops promoted him to the top spot, and the senate apparently liked him better than the guy who bought the job from the guys who’d assassinated the last guy because they sided with severus. presumably to avoid establishing the precedent that the people who murdered the emperor got to pick the next emperor lol.
and then rome had its first provincial emperor.
i still don’t understand why gladiator 2 was about whatever it’s about instead of like. the actual year of the five emperors. wasn’t that dramatic enough.