The Civil War, of course, is a vast subject. It has been studied by hundreds of scholars for nearly 150 years. In David S. Stout's examination, the historian revisits the central themes of the bloody conflict: slavery, state's rights, and the economic impact, and how each side justified their actions. Central to his argument, however, is the examination of the "just war" theory. The "just war" argument has several criteria to be "justifiable."
Here are the primary considerations, although there are many more:
1) Just cause: An immediate threat to innocent life
2) Comparative justice: The rights of one side are significantly more affected than the rights of the opposing side.
3) Right Intention: The desire to right a suffered wrong