Although SAC’s retaliation might still be devastating, it wouldn’t be quick. An estimated thirty-five to forty-five days of preparation would be necessary before an all-out nuclear attack could be launched.
Honestly, that feels like a good thing. We can vaporize people, but it requires some effort and time, so we really have to be sure we want to vaporize those people.
Here's a problem I have with the Civilization games -- no mutually assured destruction. It might not be a fun ending, but it constrains the victory conditions in a more realistic way. There should be a nuclear deterrence wonder -- enough nuclear weapons to destroy the world.
Instead, it goes with a tactical nuclear weapons model exclusively.