Call me AJ

Anti-communist sentiments were already strong in US leadership. The US didn't want communists gaining any more ground on the world stage and nuking Japan was a way to kill two birds with one bomb: end the war before the USSR entered and show the USSR that the USA could wipe out any of their cities in the blink of an eye. People sometimes try to argue that the second bomb had to be dropped because Japan didn't surrender after the first, but Japanese leadership didn't even meet to discuss the first bomb until shortly before the second dropped. At that point, losing an entire city had little effect on leadership. They already had entire cities leveled with conventional weapons. They hadn't yet processed that Hiroshima was leveled by a single bomb. It didn't matter though. The fact that they delayed at all gave America an excuse to prove to the USSR that they could do it again. The US obliterated two cities in Japan ultimately as a shot across the bow for the USSR.

What popular history likes to gloss over is the chain of events that lead to Perl Harbor. The US initially supported Japan (along with selling resources to all sides in the European war), even as Japan committed war crimes across China and Korea. The US had good relations with Japan at that point and saw Japan's invasion of China as a way to get a foothold in a country that had a history of being restrictive of foreign trade. Japan didn't roll out the red carpet for America though; they realized that they had something that the USA wanted and planned to use that to their advantage in global politics and trade. In response, the US stopped selling steel to Japan for their war effort. US leaders/strategists were very aware that cutting Japan off from resources they'd been relying on for their war would invite retaliation, and thus Perl Harbor happened. The US only ever cared about gaining greater access to markets and labor and was willing to fight a war over it, but in such a way that Japan would make the first move.

The US might have ended up on the right side of WW2, but not for the right reasons. The war in Europe was already going in the allies' favor and the entrance of the US only really expedited the war, but it gave the US a seat at the table when deciding what happened after the war. It let the US build military bases in Europe and bring more US businesses into Europe. The US suffered the least from the war and was able to take advantage of the fact that they didn't need to rebuild entire cities like every European country did. it was politically and financially beneficial to the US to join the war late on the side that was already set up to win, especially with a little extra push.