The article linked below restates the somewhat conventional wisdom that the use of nuclear weapons against Nagasaki and Hiroshima is the reason that nukes have not been used since. It is a strong argument that a nuclear taboo emerged as the years passed and the US did not use them again. The argument is, in my opinion, incomplete. It wasn’t just that those two uses were sufficient to tell the world that nukes are the most terrible of weapons and should be avoided at all costs, it was that it was only those two uses for the first uses. Imagine if Japan had capitulated prior to our use of nuclear weapons, or if the oft-suggested idea that we should have demonstrated the power of the weapons on an abandoned island inviting the Japanese to view it in an area of truce. Nobody would have seen the horror of mutilation, skeletal remains of people and structures, radiation sickness eroding people from the inside for weeks and years, etc. Arsenals of weapons would have built up so that the first wartime use, probably in Korea, would have not been just 1 or 2 relatively low yield and awkward to deliver bombs. The first wartime use could have been a dozen, two dozen, enough to take out the entire Chinese army and maybe even attempt to remove the Communist government from Beijing. We wouldn’t have the time to understand the effects of the first drops before more drops were made. Finally, the US would have certainly been attacked with nuclear weapons by the USSR in retaliation. The USSR managed to detonate their first bombs during 1949 and dropped from high-altitude bomber in 1951. They could have attacked our troops in Korea and possibly the mainland of the USA if they had accelerated production under the pressure of known US ongoing use in the war. That is, the use in Japan prevented the first use being even more widespread and devastating and possibly preventing the nuclear taboo from ever arising. We might all be dead now.