I doubt very much you would see a large scale war like WWII again, or even vietnam, I think after the futility of Iraq and Afghanistan, conventional warfare has been shown to be pretty much gone. Even with Russia rattling its saber, they have more to lose in a large scale war, not to mention the fear of it escalating into a nuclear war. On top of that, the cost of such a large scale war might be unthinkable, we spent something like 3 or 4 trillion on Iraq and Afghanistan, and those were limited wars. The wars that are being fought are going to be special forces kind of dark ops, and more and more is going to be economic and cyber warfare.