Even with somewhat assured first strike outcomes I still don't see a rational reason for a nuclear power to go ahead with it. What are they going to do afterwa

Even with somewhat assured first strike outcomes I still don't see a rational reason for a nuclear power to go ahead with it. What are they going to do afterwards, conquer territory? It's not going to work because nuclear strikes won't magically disappear the (now really angry) population. So what would be the point? And now you lose all the fruits of trade and punish your own people. Re: an insane leader ordering a strike just for fun, I have faith I guess in the staff who would be actually pushing the buttons. It has happened before.