Writing Historical Fiction

I think my thesis might be something like this...
In SPIES, when men can't watch their own back anymore, some women will have to step in and see what the enemy has in store. The main point in my book is, when men in the civil war need to seek out what the other side is doing, some women will have to step in and will need to spy on the opposing side. I haven't really started thinking what my historical fiction is going to be about because I don't really know a whole lot about the civil war. For my characters I might do a slave, a general for one of the sides, or maybe even just a wife of someone in the army. I will probably have the character living in the North where slavery didn't happen. The conflict will be that someone is fighting in the war, and gets injured and then kidnapped. My character will be trying to stop slavery by fighting for it in the Civil War.