Is anything ever justified? People do things for tons of reasons. There are lots of different codes of morals and ethics. Are any of them "right" in any absolute sense? Ask different groups of people and you'll get different answers about whether or not a particular war was justified.
Ask a hard-line traditionalist Southerner and he might say the American Civil War was justified.
A Serb might tell you the Bosnian War was justified.
An outside observer might tell you that neither of those wars were justified.
People fight wars because different groups have conflicting desires - so in that sense, every war is justified - at least in the eyes of the people who started it.