Journal of the Shenandoah Valley During the Civil War Era, out of the McCormick Civil War Institute, at Shenandoah University, doesn't pay. You'll get two copies. I generally do not work for free, & that includes my writing. The best luck I've had for cash are contests, grants, & fellowships, but I don't do Civil War pieces for those. Check out alternative routes in the history field. What can you apply to? I heard NARA offers fellowships & is a dream to visit.
There's a search bar at "Submittable," a database containing all kinds of magazines looking, topics & contests, & you can also submit directly to publishers via that. Watch out for "submission fees" and straight out scammers, but that goes for anything. Also, your local newspaper or town magazines, if you have those, could be an outlet. If your state conducts annual writing contests, say through arts or museums orgs., those can be lucrative, esp. for "exposure." The nonfiction category includes history.
Last, look into all the online resources like the AHA. They offer $100, enough for a week of lattes. You can maybe get something scholarly run in a no-pay academic journal, then later pitch an idea to an agent about a longer adaptation of your subject to a wider audience. Ask Grok & it'll list like 10 mags that pay, like JSTOR Daily, Scout Life. Keep hunting! With a wooden stake....
Good luck