USA. Oodles of natural resources, oodles of people, oodles of space, a smack of just about every major culture or topography or biome you can think of, and access to some serious military hardware to replenish my stores/give me raw materials so I can finally implement boltguns as standard issue "small arms" (boltguns are f****** big).
Also, the political system is so fucked that the people will practically beg me to hit the reset button on congress. I won't run a dictatorship, more like the existing constitutional republic but with myself as the emperor on top of it all. There's a good few small changes I can make too to prevent the system from borking itself again in a single generation. I might even be able to experiment with the system since it's not like someone's going to successfully revolt, I have the souls of my entire army on lease!
Invasion plan? Most populated states simultaneously in a massive shock and awe attack, then consolidate and focus on the few states who haven't surrendered after the national government is under my thumb.