Think, too, of the great part that is played by the unpredictable in war: think of it now, before you are actually committed to war. The longer a war lasts, the more things tend to depend on accidents. Neither you nor we can see into them: we have to abide their outcome in the dark. And when people are entering upon a war they do things the wrong way round. Action comes first, and it is only when they have already suffered that they begin to think.
Thucydides, The Peloponnesian War
We must now move from the year-to-year competition of the arms race to consider the theory of deterrence and how it may work in a crisis. We shall begin by discussing the "normal" situation of deterrence through "balance of terror," using the kind of presentation developed in Chapter 5 for the prisoners' dilemma. The true prisoners' dilemma is probably not a common situation in international politics. However, under some circumstances there are grave risks that a previously safe non‐ zero-sum situation may turn into a dangerous form of prisoners' dilemma. Nuclear deterrence always carries this risk to some degree.
The following table represents the relative values that the U.S. and Soviet governments might attach to the use of nuclear weapons in a typical noncrisis situation.