Soviets. In the new cold war, however, Russian forces achieved nuclear equality. Each side could destroy the other many times.
This fact was officially accepted in a military doctrine known as Mutual Assured Destruction, a.k.a. MAD. Mutual Assured Destruction began to emerge at the end of the Kennedy administration. MAD reflects the idea that one's population could best be protected by leaving it vulnerable so long as the other side faced comparable vulnerabilities. In short: Whoever shoots first, dies second.
From MAD to SDI
MAD acctually acknowledged more than just nuclear parity. Both sides admitted their vulnerability and prepared early thinking on a concept that later became known as "Star Wars." As early as 1961 former secretary of defense Robert McNamara said: "If we could create an umbrella we would need it, no matter what it costs."
In subsequent years, protecting strategic forces rather than the population appeared to be the morally wrong choice. When MAD lost its domestic credibility, the Reagan administration promised to work toward Mutual Assured Security (MAS) instead of relying on MAD.