Historical romances have a number of pitfalls built into them which can ruin or make the book. There are many things the writer has to know about a period in history if they want to insert their characters into it.
One issue that comes up early would be how did the people get information and communicate with those not next door? If you think about say a Jane Austen romance, we have plenty of examples interspersed throughout her books of riders who brought letters sometimes even at night. The writer doesn't have to explain how communication happens if they illustrate it in events.
In the Old West, communication was a major part of what a community would be like. It changed fast enough that a writer better know whether a community had a stage line, train tracks and regular schedule, or shipping route nearby. How did people move around?
The pony express had a brief history (April 1861-October 1862) reducing the time to get a message from East coast to West Coast down to ten days. Before that any news required either going by ship around the Horn, traveling with someone, or an equally slow route by land. After the pony express came the telegraph where at least a message could be gotten through if not a whole letter. The trains changed all of that again when packages, letters and people could be transported more safely and faster.
So to write an historical story, the writer needs to know where their area was in terms of the communication methods. Even if it doesn't seem it would relate to their own story, it does. It lends a flavor within the community. Cut off from the rest of the world is different than up on the latest events, newspapers, and magazines.
If the historical romance writer is writing a story that occurs during some other big event, maybe not even one that was directly impacting them, it's important to know. It can set a mood within one side or another within a community especially if it was a big event like the Civil War.
And going along with that, what we call an event today, like say the Civil War, might not have been the same when it was happening. When I needed to know that, I learned there were multiple names for that war but Civil War was one. So it's less confusing to use that name for the reader than to pick up a less familiar name just to prove you knew it.
Colloquial expressions are another place that can trip up the writer as we are familiar with some that seem they've always been there; but were they? I had one I wanted to use in a book. It was so good and seemed self-evident as a potential expression. When I researched it, the closest I could come to its being in usage was much later than I wanted. I used a variation but might've been safe to use it anyway since it was descriptive. The fact something is commonly used in one decade doesn't mean it was never used before.
Knowing when authors of the past were first well known can help a lot as to how their work might influence characters even those who are not particularly literate. People had a lot more knowledge of the general works of writers like say Mark Twain (b. 1835- d. 1910) than we might expect today. His newspaper articles were popular in 1865 (depending on the communication in the community) and Tom Sawyer was published in 1876; but if you are writing a story set in 1883, you better not reference Huckleberry Finn which came out in 1885. A very literate person though of 1886 might've had access to the book.
All the research needn't to make it into the romance novel because the big issues are the couple's struggles. Such research though does furnish the underpinning, the energy, the flavor, and helps with deepening the characters and the writer's own understanding of these people. Throwing facts in to prove you knew them could just lose the reader interest. Sometimes a writer can put them in casually through usage but not in some list as that just shows unsophisticated writing.
It's easier to get the kind of cloth and garments that people wore than it is to get dialogue to work for a modern reader. Some writers get the idea that they knew exactly how the people back then would think or talk. Since our only way to know such is through their old letters, journals and books, we are guessing at how they talked. A writer like Jane Austen, who was a contemporary writer to her own time, used dialogue which could come closer but maybe she just liked how it sounded. And she was only writing about a certain group of people where another community might sound quite different.
The other thing is putting our emotional needs and interests into the heads of these people from way back is okay so long as the writer knows they are doing it as part of the fantasy, the fairy tale of the romance. To kid ourselves and assume that some Native American woman of several hundred years ago would be looking at man's body and fantasizing as a woman might today is naive. Human nature is as much made up of environment and community as it is DNA. Sure we have natural yearnings and desires but a lot of what we think is much influenced by what we read, hear and those around us.
Museums can be a rich source for not only photos but stories. I particularly like to go to museums put together by those from differing backgrounds. Between that and the many books, the info on the Internet, it's possible to put together a reasonable scenario for what happened. BUT you have to look at it all with some skepticism. A good example is the story of Geronimo and how important was he in the Apache wars? I can find info to tell you whatever you want to believe and it won't match. When you go to write an historical romance, that can be handy ;).
