You can definitely get it published, its just might be harder than if you have a higher degree. It all depends on your publisher. Some require graduate degrees, some dont. Some people with Phds never publish more than one book, some people that dont even have a history degree but are knowledable on historical subjects publish dozens of books. This is actually fairly common in the military history world. Its all just down to finding the right publisher, demonstrating your work with quality writing and research, and networking with the right people.

When trying to get a work published, you need to figure out where you want it published. A small research journal for a historical society is going to be an easier task than getting a monograph published from somewhere like a university press. Some publishes go for newer historians while University presses will more than likely want decorated authors. From there its up to submitting your manuscript to the right people, making revisions, and all the fun stuff that goes along with publishing.

It definitely can be done, it just requires work on your part to demonstrate to the publisher why they should be interesting in publishing your work. Why its important to the historical discussion. Doing something thats been done before a dozen times isnt going to impress anyone, but something with a unique or more in depth view at a topic could get the attention of a publisher like a journal. Usually journals will have calls for papers and allow submittions from people of all backgrounds. They will judge your work and get back to you about revisions and possabilities about publication.