A game where you play as a Seminole in the Second Seminole War would be a perfect fit, tonally, for the Red Dead franchise. Bop around pre-Civil War Florida with a band of escaped slaves and the remnants of several tribes destroyed by the Trail of Tears, get a foothold in a new area and build up your camp over a couple chapters of side quests and world building, just as things seem to be settling in start clashing with local militias and eventually the US Army. It'll have a downer ending but not before all of the principal characters have a badass moment - write the main character as having some kind of drama with the Seminole leader that gets resolved right around when they both go down shooting and you've got the game of the year.