This is not a movie about a modern day American civil war. This is a movie about war photographers that happens to be set during an american civil war. The civil war is thematic. You will not get an in-depth history of this civil war. It's ambiguous and unimportant to the story.
This an excellent film. It's not a war movie. Though there are plenty of tense moments and action to satiate. It is an intentionally restrained movie.
This movie is a fantastic cross between "Children of Men" and "Nightcrawler." Though it may not be *quite* at the level of either, it does come close.