Will there ever be a nuclear war on a global scale?

What would the ramifications of such event (excluding the possibility of nuclear winter) be? What would the recovery entail and in what form would it most likely take?

What areas would be the worst hit? What would the fallout actually be, assuming only clean modern nuclear warheads were used? I am making the assumption the originating conflict would be between 2 superpowers with a third trying to assert control after the originating powers have been weakened by the initial conflict. If that is a poor assumption please make your own.