So learn statecraft.

Statehood has two competing and often complimentary models, the montevidean and the westphalian. Both of them are simple and helpful.

The montevidean definition of statehood posits four things; a permanent population, territory, government, and the capacity to enter into diplomatic relations.

Now, we're set on the "permanent population" bit. In fact, reams and reams of people whining about the impossibility of expatriation from our nation are avaliable. We can't just be unpedophiled. So, that permanent population is more permanent than most states - vietnam did a pretty good job of depatriating citizens of the US, I hear...

Interestingly enough, territory does not mean "undisputed territory," government does not mean "any specific modality of governance," and I'm sure diplomatic relations have already occurred in some form or another... which means that an anarchodemocratic horde who denies the legitimacy of the former united states and lays sole claim to its territories is in fact a legitimate state.

Westphalian statehood, however, is much simpler. It proposes one criterion for independence in order and draws a pair of conclusions. The axiom, of course, is independent self-determination.

AZ wrote a charming article about how we were quite aware of our independence in self-determination and exercising it from exactly that precise philosophy, to which they replied "we write neurotic rants that no one ever reads." The long and the short of it, however, is that these whiny little uncle toms who blather on and on about how "people who hate us anyway won't be our fwiendz if we don't hate ourselves" are the inverse of westphalian statehood, as they derive their order from a hostile state. It's still open to speculation as to whether they should be shot or excluded, though.

The conclusions it draws from independence of order are the equality of states and a moral principle of noninterference. The last one, otoh, went out the window very close to as soon as it was coined, with proxy wars and fifth columns all throughout europe and the cold war.

Long story short... read up on statehood. Ours is here and now. You are not under the jurisdiction of the contesting state, you are under the military force of a neighboring state, and they under yours. Exercise yours at will; we have a long history of global anarchodemocratic governance.

Once you've grasped that, you might want to look into such charming documents as the geneva conventions (minus the optional protocols), or the convention against genocide, or the convention on civil and political rights, to get some idea what to do as a state. Nonetheless, you're already there, have fun, and ffs, drive the contesting state off your land.