Japan were already on the way to surrender, the day before Nagasaki the USSR agreed to join the land invasion and that had tipped the scales to a majority of thier leadership wanting to surrender.
The fact that they were given no time to even discuss it, USSR ally with the US and the bomb being dropped is one of the issues of why it is a crime.
Also the fact many in the US military at the time wanted to do it to partly test a higher yield A bomb, and commented after thay are lucky it missed the target of the mitaubishi works as the casualty rate would have made Hiroshima look tiny.
A few factors were in play
US reluctance to the USSR getting any reach into Japan
Testing a bigger bomb.
The reluctance to Bomb Kyoto scheduled originally and to be 5 days after hiroshima.
Yes some in Japan were not ready to surrender but then they were given 3 days and preliminary info on the effects of Horishima to decide, doing it so quickly after is the crime.