"We have discovered the most terrible bomb in the history of the world. It may be the fire destruction prophesied in the Euphrates Valley Era, after Noah and his fabulous Ark.... This weapon is to be used against Japan ... [We] will use it so that military objectives and soldiers and sailors are the target and not women and children. Even if the Japs are savages, ruthless, merciless and fanatic, we as the leader of the world for the common welfare cannot drop that terrible bomb on the old capital or the new. ... The target will be a purely military one... It seems to be the most terrible thing ever discovered, but it can be made the most useful."

Harry S. Truman (1884-1972), 33rd U.S. President, (Diary, July 25, 1945)
"The World will note that the first atomic bomb was dropped on Hiroshima a military base. That was because we wished in this first attack to avoid, insofar as possible, the killing of civilians."

Harry S. Truman (1884-1972), 33rd U.S. President, (radio speech to the Nation, August 9, 1945)
".. In [July] 1945... Secretary of War [Henry L.] Stimson, visiting my headquarters in Germany, informed me that our government was preparing to drop an atomic bomb on Japan. I was one of those who felt that there were a number of cogent reasons to question the wisdom of such an act. ...The Secretary, upon giving me the news of the successful bomb test in New Mexico, and of the plan for using it, asked for my reaction, apparently expecting a vigorous assent. ...During his recitation of the relevant facts, I had been conscious of a feeling of depression and so I voiced to him my grave misgivings, first on the basis of my belief that Japan was already defeated and that dropping the bomb was completely unnecessary, and secondly because I thought that our country should avoid shocking world opinion by the use of a weapon whose employment was, I thought, no longer mandatory as a measure to save American lives.

It was my belief that Japan was, at that very moment, seeking some way to surrender with a minimum loss of 'face'. The Secretary was deeply perturbed by my attitude."
General Dwight Eisenhower, Supreme Commander of the Allied Forces in Europe and 34th U.S. President from 1952 to 1960, (Mandate For Change, p. 380)
"Mechanized civilization has just reached the ultimate stage of barbarism. In a near future, we will have to choose between mass suicide and intelligent use of scientific conquests [...] This can no longer be simply a prayer; it must become an order which goes upward from the peoples to the governments, an order to make a definitive choice between hell and reason."

Albert Camus (1913-1960), French philosopher and author, August 8, 1945
"As American Christians, we are deeply penitent for the irresponsible use already made of the atomic bomb. We are agreed that, whatever be one's judgment of the war in principle, the surprise bombings of Hiroshima and Nagasaki are morally indefensible."

The American Federal Council of Churches' Report on Atomic Warfare and the Christian Faith, 1946
"It is my opinion that the use of this barbarous weapon at Hiroshima and Nagasaki was of no material assistance in our war against Japan. " - "The lethal possibilities of atomic warfare in the future are frightening. My own feeling was that in being the first to use it, we had adopted an ethical standard common to the barbarians of the Dark Ages."

William Leahy, Chief of Staff to Presidents Franklin D. Roosevelt and Harry S. Truman (“I Was There”, p. 441)
"Completely in charge in their marble homes and granite banks from which they rob the people of the world under the pretence of bringing them culture, Watch out, for ... they'll send you out to protect their gold in wars whose weapons, rapidly developed by servile scientists, will become more and more deadly until they can with a flick of the finger tear a million of you to pieces."

Jean Paul Marat (1743-1793), Swiss-born scientist and physician and actor in the French Revolution
***
When U.S. President Harry S. Truman decided on his own to use the atom bomb, a barbarous weapon of mass destruction, against the Japanese civilian populations of the cities of Hiroshima and of Nagasaki on August 6 and on August 9, 1945, the United States sided officially on the wrong side of history. General Dwight Eisenhower, Supreme Commander of the Allied Forces in Europe and 34th U.S. President from 1952 to 1960, said it in so many words: "...the Japanese were ready to surrender and it wasn't necessary to hit them with that awful thing." (Newsweek, November 11, 1963). Between 90,000 and 120,000 people died in Hiroshima and between 60,000 and 80,000 died in Nagasaki, for a grand total of between 150,000 and 200,000 most cruel deaths.
It seems that military man Eisenhower was more ethical than Freemason small-town politician Harry S. Truman regarding the fateful decision.
In being the first country to use nuclear weapons against civilian populations, the United States was then in direct violation of internationally accepted principles of war with respect to the wholesale and indiscriminate destruction of populations. Thus, August 1945 is a most dangerous and ominous precedent that marked a new dismal beginning in the history of humanity, a big moral step backward.
In future generations, it most certainly will be considered that the use of the atom bomb against the Japanese civilian populations of Hiroshima and Nagasaki was a historic crime against humanity that will stain the reputation of the United States for centuries to come. It can also be said that President Harry S. Truman, besides lying to the American people about the whole sordid affair (see official quotes above), has left behind him a terrible moral legacy of incalculable consequences to future generations of Americans.
Many self-serving reasons have been advanced for justifying Truman's decision, such as the objective of saving the lives of American soldiers by shortening the war in the Pacific and avoiding a military invasion of Japan with a quick Japanese surrender. That surrender came on August 15, 1945 and it was made official on September 2 with the signing of the Japanese Instrument of Surrender, nearly one month after the bombing of the cities of Hiroshima and Nagasaki. Nazi Germany had capitulated on May 8, 1945 and World War II was already over in Europe. There was also the diplomatic fear that the Soviet Red Army could have invaded Japan, as they had done in Berlin, thus depriving the United States of a hard fought clear-cut victory against Japan.
But by the end of July 1945, according to military experts, the Japanese military apparatus had de facto been defeated. It is also true that the militarist Japanese Supreme Council for the Direction of the War was stalling with the aim of getting better capitulation terms hoping for a negotiated settlement, especially regarding the future role of their Emperor Hirohito as formal head of state.
In Europe, the allies had caused a recalcitrant Nazi Germany to accept an unconditional surrender and there were other military means to force the Japanese government to surrender. The convenient pretext of rushing a surrender carries no weight compared to the enormity of using the nuclear weapon on two civilian targets. And even if President Truman was anxious to demonstrate the power of the atom bomb and impress his Soviet friends—and possibly also assert himself as a political figure vis-à-vis previous President Franklin D. Roosevelt, who had died a few months earlier, on April 12, 1945—this could have been done while targeting remote Japanese military targets, not on targeting entire cities. It seems that there were no moral considerations in this most inhuman decision.
Since that fateful month of August 1945, humanity has embarked upon a disastrous nuclear arms race and is rushing toward oblivion with its eyes open and its mind closed.