What is the term used in international politics when both sides/countries/superpowers have the capacity to retaliate against an attack and to cause so much destruction that neither can afford to initiate war?

The logic of deterrence

This is called the logic of ‘deterrence’: both sides have the capacity to retaliate against an attack and to cause so much destruction that neither can afford to initiate war. Thus, the Cold War — in spite of being an intense form of rivalry between great powers — remained a ‘cold’ and not hot or shooting war. The deterrence relationship prevents war but not the rivalry between powers.