Mutual assured destruction
Mutual assured destruction (MAD) is a military strategy in which two opposing military forces are powerful enough to completely destroy each other. It should help to avoid a nuclear war.  This usually happens when both forces have nuclear weapons.  If a state attacks another with nuclear weapons, the state attacked will potentially be able to attack back. The attacker must think that he will be destroyed with his victim if he attacks. The theory is that no state would start an attack if attacking its enemy means its own destruction.