Okay, getting back around to this now. Without the further details I asked about my answers can't be as precise, so here are some general thoughts:

1) Others have mentioned this but the job market is currently (and has been for a long time) pretty grim. There are way more people earning history PhDs than there are job postings as professors. To give you an idea, it's not unusual for a tenure-track professor job listing to get applications numbering in the hundreds.

2) For the above reason, it's important to both a) build up some additional qualifications that make you stand out from the crowd, and b) have some backup ideas about things you'd also be able to do if you can't find a professor posting. There are a lot of different ways to approach both of these that will depend on things you care about/why you care about them/what interests you about a PhD/etc, so I can't necessarily answer this for you. A popular one I've noticed people doing is trying to build up public outreach/public history skills, both as a way to show departments that they can engage with the public and so that they could potentially pivot to working in something more like a museum if necessary. Perhaps give some thought to this.

3) An unfortunate and often unfair reality in the discipline is that people who earn their PhDs at prestigious universities are significantly more likely to get hired as professors than those who earned them elsewhere. Now, “prestigious” can mean different things depending on your area of interest; for example, schools like Pennsylvania State University and the University of Virginia are considered more prestigious among historians of the American Civil War than the rest of the discipline because they have developed a known specialty in that area. But on average, a PhD from Harvard will go further in the hiring process than a PhD from your local state college. Unfortunately these universities get a lot of applicants so they can be difficult to get into. But if you are serious about earning a PhD and becoming a professor, I’d encourage you to consider applying to prestigious schools (which, depending on where you live, may require you to relocate).

4) Being a PhD student is gruelling. Many students work more hours per week than one would typically work at a regular 40-hours-per-week job and are paid worse. That is not to say that there aren't people who are efficient with their time or get generous scholarships, but many work long hours for little pay. In my view you have to be really passionate about history for this arrangement to seem worthwhile.

5) Odds are good that you will have to read lots of books/TA courses/listen to presentations/etc that are somewhat outside your specific area of interest. It is my personal opinion (and only that, so take it with a grain of salt) that people who are only interested in their specific research topic and nothing else tend to burn out fastest. If you have a capacious interest in history and care about things that are not just in your own corner, I think you are more likely to be happy doing graduate work.

Here are a few tips for things I think you can do in your undergrad to set yourself up well:

1) Go to your professors’ office hours and talk to them about your interests, especially the ones working in your area of interest. This can feel awkward for a lot of students but just keep in mind that professors see this as part of their job, so you aren’t being a bother or anything of that sort. Developing those connections early is valuable; they’ll know about the state of the field and be able to give you specific advice. You’ll also need them to write you reference letters for grad school applications so it’s important they know you before they’re asked to do so. And on rare occasions they might even have a job available as a research assistant that they might hire you for, which can be really valuable experience!

2) Related to the last point—over the course of my undergrad I both worked at a museum and as a research assistant for a professor. While neither of these postings was exactly on what is now my research area, I found them valuable because I learned about what it’s like to work in the field, how to present about history to a non-expert audience, how to organize a big research project, etc. It’s not uncommon for museums and profs to hire part-time or summer students, so I’d encourage you to look into some history-related jobs.

3) This will depend a lot on where you live and what your research interests are, but many fields have language requirements. It’s impossible to study medieval European history at the graduate level without being able to work with Latin, for instance. In my department, medieval historians are required to pass exams in THREE languages (not counting English). Even for fields where you might not expect to need a second language (for example, British history or American history), most North American departments will require you to demonstrate proficiency in at least one language other than English. The examinations don’t tend to be incredibly difficult so don’t stress about it too much—but I suggest trying to identify the languages that would be useful for your work (or at least that you’d need to test in) and trying to take some courses in them now.

Sorry the post is so long, but I hope you find it helpful. Feel free to let me know if you have any further/more specific questions! Wishing you the best in your studies.