Inter-state war is by far the least common type of warfare in the modern era, although the proxy wars growing out of the Cold War muddy the waters some. Civil and ethnic warfare is much more common, and I don't think we can say that civil conflicts, at least, can always be described in terms of straightforward aggression and defense against aggression.

(Truthfully I wouldn't say that for inter-state wars either, not all of them, but they're a lot easier to spin that way.)