Yes, mutually assured destruction is a new major element since the end of WW2., that has so far prevented and all out Nuclear conflict, but as such capability now stretches beyond the superpowers (perhaps to 'would be' superpowers) even the proxies have that capability.
I was really responding to a previous poster who asked 'how close might we be to 'WW3'. The difference is of course the Ukraine situation, where recently it is being suggested in certain quarters (probably Russian propaganda) that 'tactical' ( for this read small) nuclear devices might be used by Putin if things continue as they are. Imagine if this did happen with the 'temperature' rising in the middle east as it is just now, with atrocities, war crimes, and everything else mounting, although it doesn't bear thinking about, someone should... and quickly!