Is War Just? Is it a Necessary Evil? Is it completely Uncalled For?

Since making my prior thread on personalism this begs another question. Partly inspired by hearing “Devil’s Arcade” by Bruce Springsteen on the way to work this morning (not a gigantic Springsteen fan but I do like a lot of his songs; highly suggest reading the lyrics as I think the theme of war is prevalent but that is just my analysis), what exactly do we do about the problem of war? I flutter between it’s a necessary evil to it’s completely uncalled for; I don’t think I’d ever walk around saying war is just. This makes me think of people who actively encourage war; I don’t do this. But in some circumstances isn’t it justified to defend the lives of people who can’t? I personally think that we the United States are too involved in things.