In a comment you cited your motivation as
I want to become an authority on a certain topic
What you’ll need to do to become an authority on a topic is to write and publish extensively about it. One full-length PhD thesis or book would be de rigueur, and even then I doubt you’d be considered much of an authority by most actual historians (as opposed to lay people) until you’ve published several books, or a book and multiple articles — in academia a PhD is basically table stakes.
Moreover, the publications need to carry the official stamp of legitimacy of an established bestower of academic authority: either a university (in the case of a PhD thesis), or a reputable academic press in the case of books, or reputable peer reviewed journals in the case of journal articles. Self-published work won’t count, since it won’t set you apart from the many people who think they are an authority on something but can’t get anyone to vouch that their knowledge is correct, let alone interesting.
The thing to keep in mind is that these authorities who are in a position to give you “official” credit by publishing your book or awarding you a PhD are setting the bar much higher than just you having knowledge on the topic you are writing about. For example, you may know the dates of all the battles of the Russo-Japanese war, precise numbers of casualties, and have an extensive knowledge of the political and diplomatic machinations that led to this war, etc. Still, it’s almost certain that no one would want to publish your book about this war unless you find something new to say about it, or about its connection to other historical events of the period or of other periods. In other words, having knowledge is not really sufficient, in the academic context at least, to be considered an authority. Creating knowledge is the way you gain authority.
To summarize: neither getting a PhD nor publishing offer anything other than an extremely arduous and lengthy path towards becoming an authority on a historical topic, no matter how extensive your knowledge on the topic already is. As an alternative and more feasible plan, maybe consider becoming a regular poster on history.stackexchange and acquiring a high reputation there. Perhaps it won’t be “official”, but you can still have fun and collect some concrete evidence of your knowledge and understanding isin history. Good luck!