Earlier quoted context omitted.
I don't think there is any doubt that a "preemptive" nuclear first strike by the US would have morally and legally been regarded as genocide. The last time we had a debate on HN on this topic a number of people seemed to think it would have been a good idea - which I found genuinely disturbing. Hopefully I was just being trolled.
On the other hand, there is still no universal agreement on the morality of the wartime bombing campaigns that lead to high numbers of civilian casualties.
"The total death toll as calculated by the Joint Chiefs, from a U.S. first strike aimed primarily at the Soviet Union and China, would be roughly 600 million dead. A hundred Holocausts.
I remember what I thought when I held the single sheet with the graph on it. I thought, this piece of paper should not exist. It should never have existed. Not in America. Not anywhere, ever. It depicted evil beyond any human project that had ever existed. There should be nothing on Earth, nothing real, that it referred to."
https://apjjf.org/-Daniel-Ellsberg/3222/article.html
Edit: The staggering thing about the estimate of 600 million dead was that this was known to be an underestimate as the US didn't take the thermal effects of nuclear weapons into account during planning as they were regarded as too unpredictable. Actual 'real' estimates would be over a billion dead....