Mutual Assured Destruction. A situation in which, if one side were to make a preemptive nuclear strike, they would receive a nuclear strike in retaliation from the other side, resulting in mutual destruction. One theory suggests that this risk of destruction means that MAD is a deterrent to nuclear warfare. In order to avoid MAD, a race went on behind the scenes during the Cold War period to develop a new nuclear weapon that could destroy an enemy country with a preemptive strike that eliminates the possibility of retaliation.