Deterrence is ineffective in asymmetric situations, where the opponent isn't another country but is using guerrilla warfare or terrorism.
The doctrine of 'mutually-assured destruction', as described in the previous sub-section (7.4.2.1), relies upon the symmetry of the situation. Two countries attacking each other would both be destroyed. A symmetrical retaliation would not be possible, though, if a terrorist organisation were to obtain a nuclear weapon and use it – there would be no target to aim at. Small numbers of terrorists might be dispersed over a wide area and be living anonymously among people who were unaware of their presence. Nuclear weapons and overwhelming force are therefore not a credible threat against guerrillas and terrorists. America's nuclear arsenal did not deter Al-Qaeda from bombing the twin towers.
Less obviously, perhaps, the possession of massive conventional forces is no different. Deterrence is ineffective in asymmetric situations where nuclear weapons are not involved. As described previously (7.4.1), military force is of very limited use in someone else's country: it stirs up resistance and the attackers have to go home eventually.
(This is an archive of a page intended to form part of Edition 4 of the Patterns of Power series of books. The latest versions are at book contents).