That is solely Russia, and will probably only ever be Russia. Mutual decommissioning was working pretty well for awhile, but that breaks down when fingers start getting pointed.
The US nuclear arsenal is hilariously overkill for any other conceivable scenario, and in fact encouraging smaller arsenals to "catch up" to the US is a huge liability for the country even if the maintenance was free.
And this can only be done by convincing others that they will lose should they attempt to fight it.