It's the theory of Mutually Assured Destruction that keep order as far as that goes. Now even the most podunk country is ok, as long as it's got a nuke.
I have no doubt that if we didn't have to worry about other people's nukes, and we got into a War that size today that we'd go to the nukes. We'd probably even do it quicker today, based on how soft we've gotten about face to face death as as country.