I was in the business for a while, and I’m not going to offer an opinion about to what extent mutually assured destruction prevented a third world war and whether the risks of a catastrophic event were borne out except in the hindsight that it didn’t happen yet. My views on the questions have evolved over time.
I would point out that, had the US remained the sole nuclear power, the world would possibly not have seen a lack of a major war in Europe, and that the intention of the US developing strategic weapons wasn’t to prevent war. The US didn’t volunteer nuclear technology to the Soviets in order to create detente because we wanted to balance on a knife edge for the better part of a century. The US tried to prevent the USSR from developing such weapons, and has tried experiment hard to prevent other countries from developing them. The DPRK wants weapons so they won’t be invaded. The US doesn’t want them to have weapons because we think they’ll make the situation less stable. I’m not saying the DPRK should have weapons. I’m just saying that narratives are conveniently spun to justify the things countries want to do anyway.