Hello, I’m currently a high schooler trying to size down my options of what I want to do after high school. I have a few areas I really enjoy but the one I’m most passionate about is studying WWI. I was wondering if it’s easy to make a living out of being a historian specific to this field. I’m not really interested in being a teacher but steer more towards a museum/archivist sort of deal. And how easy is it to become one, specifically if I’m a female living in the United States?
It's very, very difficult to make a career out of being a historian in any field in the United States right now. The job market is not in good shape, and universities are producing history graduates at an unsustainably high rate. Usually when people are talking about the bad job market for historians, they're talking about academic jobs (i.e. college/university teaching), which is the thing that the majority of people who go to graduate school in history are hoping to do. The situation may be a bit better on the museum/archives side of things, but not that much better. There just aren't that many jobs out there, and there are a lot of people competing for those few jobs (most academic history jobs get several hundred applicants because the backlog of un-/underemployed history PhDs is that severe).
The main place where military historians are likely to find work at this point is with the federal government, which hires historians to work in the various branches/offices of the military and perform research tasks relevant to the history of those branches. It's not like an academic teaching job where you have greater flexibility to determine the course of your own research agenda, and it's unlikely that you'll find high demand for someone who works on WWI. You don't technically need a PhD for these jobs, but everyone I know who has gotten one recently has had a PhD, which isn't surprising given the aforementioned backlog of desperate job-seeking history PhDs. And, if you haven't heard, you should not get a Ph.D. in history.
I hate to say this, but I have to recommend against trying to make a career as a historian in 2022. There are too many people competing for too few jobs, and the opportunity cost of the years you spend getting the required education for those few jobs isn't justified by the earning potential (entry-level government historical work is generally in the mid-six figures). I can't speak as much about the library and archives side of it, since that's not what I do, and maybe someone who actually works in that area can give better input on how viable the MLIS route is right now. As far as the academic/museum side of things though, it's not impossible, but it's stretching the limits of possibility.
Source: I'm a military-ish historian at a museum in the United States and a recent-ish history PhD who did three cycles of the brutal academic job market.