Why Was Harry S. Truman Justified?

As the first President, and world leader, faced with the decision of whether or not to use this technology in war, Harry S. Truman is quoted as saying, “‘I did not like the weapon. But I had no qualms if…millions of lives could be saved’” (Truman, 1973, p. 273). Despite Truman expressing peace with his decision, it is estimated that there were around 150,000 casualties in the attack on Hiroshima (O’ Malley, 2016, The Bomb section, para. 3). The question that arises from these two facts is this: what exactly were Truman’s possible courses of action, and why did he choose the one he did? Multiple sources attest to four possibilities that were on the table; these were 1.) occupy the Japanese mainland, 2.) use only conventional bombs on Japan;