As I see it, there are only two ways nuclear weapons will be used in the immediate or fairly close (50 years) future. First, an accidental firing by most likely an aging Russian weapons systems, and since most of them are still aimed at the US, a nuclear exchange could follow. (That option isn't terribly likely, but still possible) The second is with a crazy group using a small nuclear device, probably against an American city, Washington DC or New York most likely. (This too isn't very likely, but the odds go up significantly if Russia doesn't secure their arsenal or Iran goes nuclear)
The idea of any two nations starting a nuclear war is absurd. Even at the heighth of the Cold War, neither side truly wanted to, or planned on attacking the other; MAD held both sides in check. Even this holds true. The most likely country to be the US enemy in a serious war would be China; they possess about 300 nuclear weapons. That's enough to wipe out most major US bases and military complexes. In comparison, the US has about 40 times that, roughly 12,000 nuclear warheads. That's enough to turn all of China into a giant radioactive desert. Either way, both sides would lose. (It's just a matter of losing really badly, or losing really really badly) Even the Politburo isn't nuts enough to launch a nuclear attack on the US, even during a time of war, and the US wouldn't launch nukes as a first strike. MAD.
The idea of any two nations starting a nuclear war is absurd. Even at the heighth of the Cold War, neither side truly wanted to, or planned on attacking the other; MAD held both sides in check. Even this holds true. The most likely country to be the US enemy in a serious war would be China; they possess about 300 nuclear weapons. That's enough to wipe out most major US bases and military complexes. In comparison, the US has about 40 times that, roughly 12,000 nuclear warheads. That's enough to turn all of China into a giant radioactive desert. Either way, both sides would lose. (It's just a matter of losing really badly, or losing really really badly) Even the Politburo isn't nuts enough to launch a nuclear attack on the US, even during a time of war, and the US wouldn't launch nukes as a first strike. MAD.