Because war... war never changes.
You can try to play nice, and be the peaceful mediator, but eventually, you'll realise you're a lone Courier in a world forged in flame into an awful temper.
Especially when idiots who model themselves after Romans in dress but fail to understand Roman philosophy, tactics, even ethics. Sure, the Romans weren't great, but still. There's more to Rome than crucifixions and mangled Latin.
If this false Caesar was not into Romans, he might well have been into Native American stuff. Or arab stuff. Or modelled himself after the British empire. The wasteland could do with a cup of tea.
And the outcome would have been the same. A gang of mad dog killers, aping their betters from history, but failing to learn from it.
Maybe they were going for a cargo cult, by shaping themselves to be reminscent of Rome, they would attract the trappings of the rest of Rome, but alas, all they've done is proven is that their version of Rome can burn down into nothing in just one day.