While you may be lead to believe this group has control over the entire duel-state area, this is largely untrue. The Arkansas Mississippi joint-state is a collection of self reliant forts and hideouts spread vaguely around their namesake area. Although they aren't paticularly politically active, they have a fairly interesting history, and if you're in their area, it's likely you'll come in contact with them at some point.
One of the older standing organizations in the south, the Joint State began operating not long after the smoke cleared from the great war itself. Remnants of the actual government, or so they claimed, in Arkansas where prudent in the first days after the war, deftly manuevering loopholes and opportunities to bring the last few pieces of the national guard under their disposal. Using them as a buffering force against the hordes of scrambling survivors was the perferred tactic, protecting those that they could and letting the rest wander the wreckage of Little Rock. As time passed, any possible fat was cut, and few remained. With the dust cleared, small strands of the Arkansas state government survived, and among them one rose. Ashland Trufield, the master architect from the begining, turned out to be nothing more then the postmaster of Arkansas.
The years left the Arkansas government on it's own as entirely unstable, and out of necessity, it aiding the clinging remains of another state government to help it's own stability. With what was left of Mississipi enlisted as a sort of working class, the newly formed Joint state seeked what it felt most important, stability, and it did so by forcing the old constraints of government into what equaited to a basic system of feudalism. With the Postmaster as it's vaguely representative king and the position of Mayor turned more into an elected Baron of local lands then anything else, the joint-state set about fortifying it's spread lands and settlements and has been sitting on them ever since.
With their modern guards and soldiers still called "Nationals" turned inward instead of outward, you likely won't gain much trouble unless you stumble into one of their towns or settlements. Laws are generally strict in the interest of protection, and you should expect nothing less then a search before you can enter. The Joint-State may not offer many freedoms, but it's a safe life, and many hold with it for that reason.