The fear is not that they will use nukes during the collapse, but that after the collapse, there will be multiple smaller nations, each with their own supply of

The fear is not that they will use nukes during the collapse, but that after the collapse, there will be multiple smaller nations, each with their own supply of nukes and unpredictable governments. This was also a concern during the collapse of the Soviet Union, and the US government worked closely with the USSR government to make sure that all nuclear weapons remain within Russia. In particular, Ukraine was forced/convinced to give up its nuclear arsenal.