This is my view on it as a non-economist. Feel free to rip into it:
Well at it's core, war doesn't really produce anything of use for the economy. It stimulates research which can then lead to technologies sold to other countries (ie. giving us money), but war specifically doesn't really help us. We have to use resources to build guns and then kill other people who we could potentially use (to some extent). It causes employment, but in a fashion which is really just redistributing wealth we already have (at a loss due to the fact that some wealth goes into making bullets/tanks/etc. which really doesn't directly help us). But then there's a lot of other factors to consider, since our defeating others can potentially give us more than we initially spent. It's not exactly an easy question to answer and people will say different things since a "healthy" economy isn't easy to specify. But most importantly, as long as there is a shortage of resources (ie. a finite amount), there will be inequity and war (or at least some conflict of some sort), so it's not going away anytime soon.