Since the advent of nuclear weapons in 1945, deterrence has taken on a special meaning. Today if a state chooses to resort to violence against a nuclear state, there is the possibility that nuclear weapons will be launched against it in retaliation. If this happens, the cost of the aggression will be unacceptable, especially if both states have nuclear weapons, in which case the viability of both societies will be at stake. Theoretically, therefore, states that recognize the destructive capability of nuclear weapons and know that others have a second-strike capability—the ability to retaliate even after an attack has been launched by an opponent—-will refrain from taking aggressive action, using its first-strike capability. Deterrence is then successful.