If you're an optimist, there is the view that neither side of the Cold War wanted to die. Excluding the truly religious people who believe that dying and going to heaven is better than being alive, most people want to avoid their own deaths. When politicians believed they could send soldiers off to kill without risking their own lives, they started wars. But since ICBMs meant than starting a ground war against a nuclear power put the leaders at risk, the leaders chose relative peace and deescalated when possible.