You folks need to read more about the Civil War. It was an intensely bloody conflict. The year the war ended, the largest budget item in Mississippi was for prosthetic legs and arms. Each side truly believed in what they are fighting for and that makes for bitter fighting. Sure, by European standards it was short, but unlike some of the European wars, it was constant.
The Civil War was also the first modern conflict in many ways and at the end devolved into trench warfare that was seen also in WWI. It became different and bloodier because of this.