Why Would You Launch a Nuclear Weapon?

The idea that one country fires nukes targeting a civilian base, and then the other country responds by blowing up the other country' civilians makes no sense at all. Only if they're targeting another ideological nation do you get mutually assured destruction in the event of russia. But see, mutually sured, whatmton to sayis, mutually sure destruction is a doctrine that only applies once you've launched a nuclear weapon. It's not going to stop anything, but certainly you can kill a bunch of innocent people.