If a major war is declared, will the gods come down and forcibly push The Big Red Button if we don't? The premise of this question is ridiculous.
Nothing has to be a certain way.
Perhaps this was no the framer's intent. What the framer might have meant to say is "will the next major war most likely be nuclear?"
My answer is still no. What are wars fought over? Power. Resources. People. Land. Nuclear weapons make war meaningless. What is the point of power if there is no one left to acknowledge it? What is the point of resources if all the machinery that uses the resources are destroyed? What is the point of warring over people if all the people are dead? What is the point of owning more land if the land is an irradiated uninhabitable wasteland?
No, if there is something important enough to fight a major war over, all sides involved will take extra care to make sure nuclear weapons are not used.
Computer and economic, it's going on as we speak.
The damage to an economy can be just as major as an conventional attack and is easier to hide, infrastructure and the economy are the current targets of choice I think. So the nuclear war has effectively been skipped, next will be nanites possibly.