Successful writers need to publish a book. When you are dealing with a niche market, the problem is not the market itself, but the market to get to that market. If you are writing about a small market such as Transylvanian history, there are possibly one or two small presses who might take an interest in your writing.
However, should you chose to, you can write and self-publish your book about Transylvania, Romania in a fairly short time frame. This leads to the question of market saturation. If you go over to Amazon.com, most of the books about Transylvania, and the history of the area, are written by a few people. Some authors even have several books on the market for people to purchase. Looking deeper, it is possible to see that a few of these authors are successful in a niche market, but most are not.
The possibility for the lack of success of most authors comes from a basic economic tool: supply and demand. There are a lot of travel books published about Romania and the many Eastern European countries around it, and these do well, but should a person who self-publishes a book try to get a small corner of this market, the chances are high that they will fail. What's the reason for this? There is already a good supply of travel books out there that met the demand for tourists. Also, most tourists are more likely to rely on a brand name published book, such as Lonely Planet, and not something that is self-published by an unknown author.
Travel books are hard to write, and they are also hard to market. Most writers will tell you that writing a book is hard enough, but what about writing fiction on Transylvania?
If you were to write a fiction book about Transylvania, you are faced with stiff competition in this marketplace. The simple fact is that fiction about Transylvania is already saturated with novels on Dracula, or some other legendary figure. Most readers who are interested in the area have read Bram Stoker's Dracula or have seen many movies about vampires or the area. There isn't a lot of romantic fiction, but there is also not a demand for this style of book from readers. There are self-published authors out there, but they are also focusing on Dracula or some other dark element of Transylvania. In this case, yes, the self-publishing on Transylvania is overdone, and there isn't a lot of choice out there.
The history of Transylvania might be the area where a self-published author should see some form of success with their creative writing. When you spend some time looking at Amazon.com, you'll get a good grasp of how much of a niche market this subject area really is.
A quick look at twenty history books about Transylvania showed that most are not long — about 60-200 pages — and almost all of them are self-published. Some of them are available for no cost, and some are offered for only 99 cents. Clearly, this means the market is full, but not over-saturated. It looks that way when you simply add the search term "Transylvania" that there is a lot of choice, but 6,333 search results in all departments is not a lot based on such a general term.
In books, using the same search term, there were 1,936 books linked to the word "Transylvania". If you base your success on the fact that a reader will find your book on Amazon since there isn't much competition, think about the fact that there are over 8 million books and counting on Amazon.com. To reach a reader in given subject area, you will have to market on your blog or website.
This seems easy, but break this down even more. According to some self-published writers, including Aaron Shepard and Dan Poynter, most writers, be they traditionally published or self-published, don't sell a lot of books. Some quote the number of books sold as a self-published book to be about 41 books outside of family and friends. If there are already a lot of writers out there with books on Transylvania, and many of them are targeted to a niche market, it is likely that they sell reasonably well, but not exceptionally well.
Most of the books that are found in the subcategory of Transylvania are specialized. If you self-publish there, you will find the books are short and are a part of a series. This makes it seem as if there are a lot more books out there. If you're looking for a book on the history of the Transylvanian Saxons, you will find about 15 which match this criterion, of these books, I would estimate there are about 5 unique authors, and most of them self-published their book. Most have had readers purchase a book, and most are reasonably priced.
The deeper into specific areas of the history of Transylvania a reader goes, the more likely the book is self-published, and the more likely that market is over-saturated with writers. In this area, yes, self-publishing on Transylvania is overdone because of the niche market's nature.