During the Cold War, both sides possessed weapons of mass destruction, but neither side used them, deterred by what was known as MAD, mutual assured destruction. Similar constraints have no doubt prevented their use in the confrontation between India and Pakistan. In our own day a new such confrontation seems to be looming between a nuclear-armed Iran and its favorite enemies, named by the late Ayatollah Khomeini as the Great Satan and the Little Satan, i.e., the United States and Israel. Against the U.S. the bombs might be delivered by terrorists, a method having the advantage of bearing no return address. Against Israel, the target is small enough to attempt obliteration by direct bombardment.
It seems increasingly likely that the Iranians either have or very soon will have nuclear weapons at their disposal, thanks to their own researches (which began some 15 years ago), to some of their obliging neighbors, and to the ever-helpful rulers of North Korea. The language used by Iranian President Ahmadinejad would seem to indicate the reality and indeed the imminence of this threat.
Would the same constraints, the same fear of mutual assured destruction, restrain a nuclear-armed Iran from using such weapons against the U.S. or against Israel?