Double deterrence: Two challengers, one defender

Author: Dr. Frank Zagare (University of Buffalo)

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During the cold war the conventional wisdom was that an all-out war between the United States and the
Soviet Union was all but precluded. The key to this strategic nirvana was a carefully calibrated balance of
strategic weapons and the high costs associated with nuclear conflict. The policy that was credited to
bringing this state of affairs about was labeled Mutual Assured Destruction, or MAD. Each side threatened
to obliterate the other if it were attacked. Based on this logic, some strategic thinkers argued for the
selective proliferation of nuclear weapons, to Iran for example, in order to stabilize the relationship
between two otherwise hostile states (Waltz, 2012). Others argued that Ukraine was misguided to have
surrendered its nuclear arsenal in 1994 (Mearsheimer, 1993).

However, the theory underlying this policy, sometimes called Classical (or inappropriately, rational)
Deterrence Theory, does not pass the test of strict logic (Zagare, 1996). It assumes, simultaneously, that
the players are both rational and irrational—rational when they are being deterred and irrational when
they are deterring. Bernard Brodie, considered by many to be the seminal deterrence theorist, put it this
way: “For the sake of deterrence before hostilities, the enemy must expect us to be vindictive and
irrational if he attacks us” (Brodie, 1959, p. 293). The noted game theorist, Thomas Schelling, who was the
recipient of the 2005 Nobel Prize in economics, also argued that nuclear deterrence only worked if an
aggressor was convinced that its opponent would retaliate—irrationally. As he wrote so succinctly: “…
another paradox of deterrence is that it does not always help to be, or to be believed to be, fully rational,
cool headed, and in control of one’s country.” In other words, it was rational to be irrational (Schelling,
1966: 37).

Logically inconsistent theories are prima facie seductive, yet fatally flawed. They invite theorists with a
point of view to draw almost any conclusion, including its exact opposite, depending on the analyst’s
policy preferences. So, it is unsurprising that other classical deterrence theorists, working from the same
set of assumptions, oppose disseminating nuclear weapons to Iran or to any other state actor including
Ukraine.

To overcome the logical inconsistency of Classical Deterrence Theory, Marc Kilgour and I have constructed an alternative theory that insists that the players are rational (or purposeful) at all times. We call it Perfect Deterrence Theory (Zagare and Kilgour, 2000). In this alternative specification there are certain conditions under which wars cannot be avoided. For example, it is possible that Russia may still have invaded Ukraine even if the Ukrainians had not given up their nuclear capability once the Soviet Union broke up. Low level conflicts are very difficult to deter, as are situations where one state seeks to deter an attack on an ally. Worse still is the propensity of these conflicts to escalate. Sunk costs may play a role here. But so may uncertainty about the extent of resistance, if any. Risk taking leaders are the most dangerous.

For obvious reasons, both Classical Deterrence Theory and Perfect Deterrence Theory have focused on
dyadic relationships. It is clear, however, that that focus now needs adjustment. In the current
environment, there are currently two dissatisfied major nuclear powers that would prefer, ceteris paribus,
an adjustment of the rules that support the international political and economic system as it operates
today. At the global level, then, a key question is how a defender of the status quo might deal with two
potential challengers.

The answer to this question depends, in part, on the relationship of the two challengers. There are three
possibilities:

1. Both dissatisfied actors act independently in separate disputes. If this is the case, there is no need for
   new theory. Current theory still applies. Assuming that the conditions needed to deter the most
   problematic case are met, these same requirements would suffice to deter the less problematic case
   as well. The assumption of independence implies that it is highly unlikely that the two disputes would break out simultaneously.
2. Both actors operate as one in a tacit alliance. Again, current theory can handle this case, as it did
   during the Cold War.
3. The second (secondary) actor (Challenger 2) becomes a player if and only if the primary actor
   (Challenger 1) upsets the status quo. It is clear that it is this special situation that requires further
   scrutiny.

The purpose of this essay is to extend the logic of Perfect Deterrence Theory to the third case, which, for expository purposes, will be referred to as the three-body problem.

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