A state may arm itself with purely defensive intention yet, provided its forces are judged capable of attack, those states within range will feel unable to disregard this possibility and be obliged, perhaps reluctantly, to add to their own arsenals. So arises what John H. Herz (1950) identified as the security dilemma. Anticipated at least as early as the seventeenth century in Lord Rochester's ‘Satyr against Mankind’, this insight began to be modelled by game theorists as an instance of Prisoners' Dilemma in the 1970s. A formal approach makes explicit the structure of the dilemma, which is that two independent states cannot attain the security both desire at least joint cost because each must guard against the heavy costs it will suffer should the other cheat.
Thus fear may prove a more pervasive and fundamental general cause of war than aggression. Many realists regard the dilemma as insurmountable. Optimists have argued that trust between states may be developed, and the dilemma surmounted, by means as varied as repeated interaction (Robert Axelrod) or efficacious grace (Herbert Butterfield). See also arms races.