If its either nuking the entirety of the other country or being enslaved by the despotic regime of the that other country...at least with the US, I can guarantee you its the former every time.
The USA already proved it needs FAR less incentive than all but guaranteed enslavement by another country in order to resort to nuking said country.
A smaller casualty count for its army is more than sufficient.
No disagreement, but lets be fair: The countries with the so-called "No First Use Policy"....that is pure pretense. If put in the same situation as the United States was in, they would use it in a heartbeat. In the end, it was the right decision by any calculus you want to use in that it saved both Japanese and American lives and brought forth the inevitable conclusion of American victory.