A common misconception about the study of history is that historians figure out what happened based on some concrete facts and evidence, and they write about events exactly as they happened. This, unfortunately, is usually not the case.
One main reason for this is that humans have always behaved like humans. That is, they’re sometimes unreliable. Whenever someone documents something, there is a chance they’ll lie, embellish, or remember things incorrectly. Therefore, historical facts are not as concrete as we’d like them to be because the evidence is not always reliable. This is especially tricky in the pre-modern era (roughly to 1500) when literacy was not a widespread skill, and, for the most part, only those of a privileged class could read and write. Historians may have only one or two primary documents dealing with a certain issue at a certain time, and it’s hard to tell how truthful those documents were. For example, there were a lot of crazy things written about some Roman Emperors, but those accounts were written by politicians who didn’t like that particular emperor and may very well have written untrue things about them. Did Nero really burn Rome? We’ll never know.
One more thing: interpretations of history change fairly frequently. As more women and minorities got access to education and became historians, new methods and historical topics of study emerged. By way of another example, up until the 1980s, the idea of the “happy slave” was still prevalent in historical narratives. Eventually, historians interested in the lives of slaves, rather than slave-owners, challenged that idea and now it’s no longer accepted as historical fact that some slaves were happy with their ordeals.
So what does all of this have to do with creative writing? My point is that if you want to write accurately about history, you need to dig deep. There are many historical inaccuracies that people accept as truths, and if you make it your goal to write as factually as possible, you’ll need to do your homework about those inaccuracies.
This all may seem intimidating. Where does one start when attempting to find accurate, reliable historical research? Believe it or not, Wikipedia is not a bad place to start. If you look up a Wikipedia article, it will often state whether historians have doubts about something or another in regards to that topic. Of course, you should not begin and end your research with Wikipedia, but Wikipedia is a good springboard. Furthermore, the sources they use are often quite good.
The Internet is great, but I also advocate for going to a good, old-fashioned library. When considering history, books are often more reliable than the internet. However, be careful not to rely solely on books that are more than 20 years old or so because, as I mentioned earlier, historical ideas and interpretations often go out of date.
Do remember not to get too caught up in details, though. If you are writing fiction, then facts are pliable. Don’t let getting something exactly right keep you from writing something brilliant!