I don't really know anything about the American Civil War. It was from 1861-65 (I just looked that up) and more or less between North and South. But, what I find most compelling in looking at civil war photographs, is that not knowing anything doesn't really matter much. You can still look into the faces of these men (and sometimes women) who lived 150 years ago and be moved. This is the first major conflict since photography was invented, which makes it all the more striking. For the first time, we can see the men who fought and died, see that wartime sad look in their eyes. We can see the real people. It is also so shocking to see the youth of some of these men-- boys, not even men, teenagers a lot of them. So interesting, and so sad.
These are all from the Library of Congress's massive collection-- here, to see them on their site, and here for the Flickr Commons collection of the same photographs. I'm going to link to the Flickr Commons ones.
I'm not going to say anything more, because this is about looking into the faces of a hundred and fifty years ago, and seeing people who at heart are just the same as those alive today.