It may be the best part of writing the genre–the chance to really learn about the people. It is also an essential part of writing historical fiction. I am often asked how to go about it.
That’s a hard question to answer because it depends on what period you are researching and whether you are starting from knowing nothing about the period (except that you want to write about it) or any range from knowing a little to being an expert. My first advice is to not depend on Wikipedia. That can be a good starting point to get a list of resources and a general overview. Then you need books. I do consider the sources listed in Wikipedia to be an excellent starting point, however, so I am not totally discounting it.
As much as possible, I strongly recommend depending on original (sometimes called primary) sources. These are sources produced within the time period you are studying. While this term can be fuzzy, for fiction purposes I don’t think you need to draw too fine a line. As an example from my own work, I consider The Brus by Johne Barbour to be a primary source even though it was written about forty years after the death of Robert the Bruce. A historian might quibble that he wasn’t at the events he chronicled. Well, neither were the friars who wrote The Chronicle of Lanercost which was exactly contemporaneous. Both, however, talked to people who were at those events.
All sources, both original and secondary, have to be looked at with an awareness that they had a certain specific political viewpoint. The Chronicle of Lanercost, for example, was written by friars who believed in the right of the English to conquer Scotland, and Lanercost was occupied by and paid tribute to Scottish armies. They could hardly be expected to be friendly to the Scottish cause. Barbour was, of course, a loyal Scot with good political reason for praising the Bruces and the Douglases.
This does not invalidate what they have to say, but has to be taken into consideration with ALL sources. I know of no historical period that doesn’t involve controversy. Later secondary sources might, for example, want to denigrate the independence of Scotland or defend Scotland’s right to independence as well, so political opinions have to be weighed when sources differ. And you can bet sources are going to differ!
Of course, there is also the difficulties of translations. Some source material is difficult to find in translation if you don’t read the original language and translations can (translators being human) contain errors. Some source material is impossible to find and you at times have no choice but to depend on secondary sources.
If you wondered, in my own work about the Scottish War of Independence, I used a pretty wide range of sources. I’ve mentioned The Brus (or The Bruce) and The Chronicle of Lanercost. I also used as primary sources Bower’s Scoticronicon, The Chronicle of Walter of Guisborough, and The Chronicles of John of Fordun. Some of this material was not easy to obtain.
For secondary sources I used G. W. S. Barrow’s Robert Bruce & the Community of the Realm of Scotland (a wonderful work), Barron’s The Scottish War of Independence, Ronald McNair Scott’s Robert the Bruce, King of the Scots and I. M. Davis’s The Black Douglas.
Of course, the fact that one is telling a story must not get lost in the history, but the history has to be part and parcel of the story.
Or that is my theory anyway.