Here is one source which details some of the questions being raised https://nationalpost.com/news/did-the-atomic-bombings-of-hir...
However I was probably wrong in saying most historians disagree, it seems there is still significant debate https://www.historyextra.com/period/second-world-war/atomic-...
The manhattan project involved The US, Canada, The UK and it was headed by a captured German scientist. When the project started the goal was to try to beat Hilter. Near the end of the war the US tanks never went into Berlin. The peace deal signed after the war gave up too much and the Russians never lived up to it creating the conditions for the cold war. The US was hopeful at the time.
An extended war with Japan would cost millions of lives. Japan was never going to give up as they were run by a crazy group at the time. Remember after they dropped the first bomb they refused to quit. The H-Bomb was the only thing that forced them to give up.
"Truman stated that his decision to drop the bomb was purely military. A Normandy-type amphibious landing would have cost an estimated million casualties. Truman believed that the bombs saved Japanese lives as well. Prolonging the war was not an option for the President. Over 3,500 Japanese kamikaze raids had already wrought great destruction and loss of American lives."