This is a conspiracy theory that historians have been fighting against for decades. There is no documentary evidence this was the thought process, and all the people involved always denied it.
Let me tell you a little story...
My wife and I visited Japan a year or two before the pandemic. As we always do, we compromised on our activities while there. I prefer history and high culture; she tends to prefer "urban exploration" or natural beauty. With one of "my" days we visited Hiroshima and the Hiroshima Peace Memorial.
It's a hard place to visit. Up there with the
Sachsenhausen concentration camp we went to outside Berlin. Most people killed or wounded by the atomic bomb were civilians -- women, children, and the elderly with young men in military or industrial service somewhere else. Few of them individually did anything to deserve a nuclear weapon being dropped on them. They were going about their lives and trying to serve their nation, even if their nation somehow went insane in the 1930s and deserved what it received for it.
One note at the memorial enraged me, though, and it does to this day. It read something like --
"Hundreds of thousands of Japanese civilians were the first victims of the geopolitical conflict between the U.S. and USSR that would come to be known as the Cold War. President Truman dropped the bomb on Hiroshima as a demonstration of American power and influence to the Soviet Union."
NO ******* WAY! **** YOU!
Truman dropped the bomb because the prospect of invading Japan was terrifying. Japan was an advanced and cultured nation before the war but, again, somehow went insane as a society. The atrocities committed in Korea, China, Indochina, and the South Pacific are every bit as bad as the ones the Germans committed in Europe and the Soviets against their own people and eastern Europe. Worst of all, they refused to admit when they were beaten to the point they were willing to commit national suicide before accepting defeat and indignity. In such a difficult situation, Truman did the rational thing we probably would have all done and decided to exhaust all other options before invasion -- so drop the big one and level a few cities of theirs.
See if that snaps them out of it.
Japan wasn't an innocent victim caught in the crossfire. They received what they deserved. Societies being unable to acknowledge and move on from past atrocities leads to present pathologies.
It is a stupid point anyways. To writ --
(1.) Truman didn't even know about the bomb until
after he became president. There's this story about Henry Stinson, FDR's old Secretary of War, asking Truman to stay for five minutes after his first cabinet meeting as president and only then telling him about the Manhattan Project.
Which I bring up because...
(2.) Stalin already knew about the bomb when the U.S. dropped it on Hiroshima. He knew about the Manhattan Project in the early 1940s while Truman did not learn of it until early 1945. The NKVD had the project leaking like a sieve. There
were many secret communists involved, though Oppenheimer was not one of them. There was not anything to be gained by a "demonstration" -- Stalin knew everything already.