I’d be interested to hear how you imagine an event being arranged. Would you have characters from both “sides” coming together? Would they be in direct conflict, or perhaps meeting under some sort of truce?
I ask because a truce sounds unlikely given how aggressive the Empire sounds, but open conflict would quickly result in lots of dead PCs.
My idea for a compromise is that the campaign could consist of a series of clandestine meetings between the League and members of the Army who may have interests in common. For example, there could be a popular uprising happening against the Empire in the country where the game is set (NZ?), which is making some members of the Army worried that they’re about to be overthrown, and therefore potentially open to the idea of joining forces with the League so that they’re on the right side of history when the Empire bigwigs are put against the wall. However, they’re not completely convinced yet, and some of them may be informants for the Queen.
To give a historical analogue, this might be something like the Amercian Revolution. Some people in the country are loyal to the Empire, some are opposed to it, and some are trying to figure out how to come out on top when the dust settles. To follow that analogy, instead of secret meetings these could be official meetings between various movers and shakers in the colony, some of whom are loyal to the Queen, some are secretly members of the League, some are on the fence, some are loyalists pretending to be on the fence so they can uncover the plans of the League, etc. In the American Revolution meetings just like that changed from “how to rule the colony for the Empire” into “whether and how to declare independence”, with the loyalists naturally shouting about treachery against King George at this shift in the official agenda. This approach might work well for you, as it gives the game a strong structure based on the passage of declarations and laws via some official process, with secret meetings happening around the official ones, and plenty of pomp and ceremony which is appropriate for the Victoriana theme.
Either of the options I’ve outlined would probably work well with pregen PCs over a short campaign of events, each one being a meeting. You could probably do it in three events or so.
Unless perhaps you’re imagining less of a intrigue game, and more of a survivalist warfare type thing focused on the action in the ruined colony? In which case, it might be more like a series of linear adventures with your players taking turns playing NPCs for each other to kill, leading up to a final event where the PCs confront each other.
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