Countries with atomic weapons have never invaded another country with atomic weapons. This is a great improvement over WWI and WWII, although it is hard to know what the long tail risk is of killing almost everybody with a full scale nuclear exchange and nuclear winter. I think maybe the best situation would be that each responsible (to be determined) country would be allowed 10-30 nukes on ICBMs only (verified somehow; live cameras plus inspections?). With nukes on ICBMs only there would be no sneak attack where the attacker is unknown. With a small number of nukes, deterrence is still likely and the possibility of a nuclear winter is eliminated. I'd trust Norway with a small nuclear arsenal.