Even international alliances can unravel when nations confront the insanity of a nuclear holocaust.  This is what happened recently when the Russian government threatened Ukraine and other nations with nuclear war, only to be rebuffed by its Chinese ally.  Much the same thing happened in the late 1950s and early 1960s, when, ironically, the role of the two governments was reversed.  These incidents demonstrate not only that nuclear deterrence is unstable, but that, while nuclear weapons exist, the world remains in peril.