I started out as an actuarial science major but got weeded out by the weed-out course at my university (Calculus II), so I changed my major to history because it was what I was good at in high school and was my primary area of intellectual interest. I studied Russian history as an undergrad but didn't learn much Russian because my university quit offering it after my freshman year. I went to grad school in history (focusing on Modern Europe and Holocaust Studies) because I had no real marketable skills but I was good at school, so more school seemed less scary than the real world. I graduated in five years, and ended up with a good job essentially through dumb luck, thanks to a series of chance encounters in grad school getting me a foot in the door at the museum where I currently work as a research historian, and was able to publish my dissertation as a book a couple of years ago.

To become a professional historian, you'll need to follow those steps (in a more organized and deliberate manner than I did), starting with an undergraduate degree in history. At one time, an undergrad degree was sufficient for some jobs, but nowadays most jobs will expect you to have a master's, if not a Ph.D., for you to even be considered. That means you'll have to go through the process of applying to grad schools (which can be a frustrating and opaque process), finishing your graduate coursework, taking your comprehensive exams in your field(s), developing the requisite language and research skills, and then writing and defending a dissertation. Nowadays, there's generally an expectation that you'll publish something (a journal article, a book chapter, etc.) as a grad student, and once you graduate, you'll work on turning your dissertation into a book that will be published by an academic publisher (e.g. a university press). After that, you're ready to hit the history job market.

And now, the moment you've all been waiting for...the patent-pending u/warneagle Why You Should Not Go to School for History in 2022 Rant™!

You should not go to school for history in 2022. The job market in history is incredibly bad right now. It cratered in after the recession in 2008, recovered somewhat for a few years, and then tanked once again, and hasn't recovered since. In particular, the number of tenure-track teaching jobs is dwindling due to declining history enrollments; people don't enroll as history majors because there are no jobs, enrollments declining means fewer teaching jobs, no jobs mean fewer students enrolling...it's a self-perpetuating cycle that doesn't seem likely to end anytime soon. Even if you successfully finished a Ph.D. at a top institution (the top 10-15 schools produce the majority of TT faculty), competition for the few available TT jobs is extremely intense; most of them receive literally hundreds of applications, because the American education system is churning out about 3 Ph.D.s for every new TT job, which means there are several years' worth of Ph.D.s fighting for those jobs along with the newly-minted ones. The traditional academic career path (get Ph.D., get TT job, publish books, get tenure, be set for life) is essentially dead and probably isn't coming back. The job market outside of teaching isn't much better. You have the same level of fierce competition for every job, plus the fact that some jobs are restricted to people with specialized training (e.g. in library or archival work). Your chances of landing one of these jobs are not good, and these jobs are also dwindling, although not as precipitously as TT teaching jobs.

For most history Ph.D.s, the years following graduation consist of stringing together low-paying adjunct teaching jobs (most of which offer little in the way of benefits) and postdoctoral fellowships while hoping to break through on the academic job market. Most of them never do and end up going to do something else, having wasted a decade or more of the most productive years of their lives. The odds of getting a TT job or another type of academic position in history are simply not good enough to justify going to grad school as a career decision. Getting a degree that won't get you a job is bad on its own, but it's even worse when you consider the opportunity cost of those years you could've been working and building a resume instead of toiling away in grad school for a degree that doesn't help you. Some people who are either naïve or old enough to be out of touch with the current reality will tell you that the skills you develop as a history student will help you get another job even if you don't get an academic job in history, but the reality is that most of those skills are soft skills that don't really immediately qualify you for anything. The tradeoffs are simply not worth the investment considering the state of the job market in 2022 and the fact that it will probably only get worse from here.

As far as writing a book goes, it's certainly easier to publish a book than to get a TT job (in fact, a book or book contract is generally a prerequisite for getting a TT job, rather than what you did after starting your TT job like it was in the old days), but it's still a difficult process to succeed in. You'll spend several years working on your dissertation and your committee will pass you at your defense and tell you how great it is, but the reality is, in an acquisitions editor's eyes, your dissertation sucks. Everyone's dissertation sucks. It takes lots of time and work to turn a dissertation into a publishable book (I finished my Ph.D. in May 2016 and my book based on it came out in May 2020, and that was considered relatively fast). Historical research and writing can be fun and rewarding, but it's also mentally exhausting because you're adding it onto your other professional duties (if you're lucky enough to get a job, that is). I certainly wouldn't discourage people from researching historical topics they're interested in (otherwise this sub wouldn't exist) but the world of academic publishing is arcane and difficult to navigate, and publishing peer-reviewed scholarship is time and effort-intensive.

I'm sorry that I replied to your post about your career ambitions and then spent the bulk of my comment crushing your hopes and dreams, but this is the harsh truth that you (and anyone else considering a similar career path) need to hear. Yes, it would be much nicer of me to say "go for it, you can do anything you set your mind to", but I know from my own experience and that of so many of my peers and friends that that's simply not true; you can do all the "right" things and still get left holding the bag after you graduate. Yes, this is absolutely hypocritical of me, since I did the exact thing I'm telling you not to do, but I'm telling you the things that I learned the hard way because I don't want to see someone make the same mistakes that I did. It's cynical and negative and pessimistic, but it's the way things are for historians right now. You'd be better served making a career somewhere else and pursuing your interest in history on the side; take all the history electives you want in school and do all the reading and research you want in your free time. Just don't try to make a living out of it, because it's just not a viable career path in 2022 or the foreseeable future.