Germany and Italy were gone, defeated. From 7 May, 1945 WWII was essentially the 51 nations of the Allies vs. Japan. A pretty evenly matched war, if you ask me... The explanation for Truman's decision was for a political purpose.
Roosevelt had made a deal with Stalin that Russia would interfere in the Pacific War within 3 months after the war in Europe had ended. Truman was against this. He did not want to see communist Russia staking claims all over Asia like they were doing in Europe.
This virtually ruled out the possibility of the US co-operating with Russia to end WWII. With no navy, no air force, their armies losing in China, their people at home starving to death, American bombers ruling their skies, an effective American sea blockade in place, Russia having just declared war on them, and with martial law imposed, Japan was essentially defeated by August 1945. No atomic bombs or a costly US invasion was militarily necessary to end WWII.
Truman dropped atomic bombs in a frantic attempt to end the war before Russia could rapidly acquire territory. Truman's policy to contain communism in Asia was crystal clear. Just six days after WWII, the Americans landed in South Korea to prevent the Russian advance.
Ironically, it wasn't the atomic bombs that ended the war but the Russian declaration of war on Japan followed by the subsequent Russian invasion of Manchuria. Prior to August 9, 1945 Japan had been trying to capitalize on Russia's neutal status by using them as a negotiator to end the war. The Russian intervention on the side of the Allies all but ended that option, which is why the Russian declaration of war on Japan had a profound effect in ending WWII.
Another reason for Truman's decision was researching nuclear weaponry. A uranium-type bomb was dropped on Hiroshima and a plutonium-type bomb was dropped on Nagasaki. Truman wanted to compare the power of these two bombs on whole cities (hence the reason why Hiroshima, Kokura and Nagasaki were deliberately left free from conventional bombing).
After the war Truman set up the Atomic Bomb Casualty Commission (ABCC) which studied the victims of Hiroshima and Nagasaki for research purposes. The victims were given no medical treatment whatsoever. All this is clear evidence of Truman's intention to study the effects of nuclear weaponry - on both cities and people.
If I was President of the USA I would've waited until the Russians declared war on Japan on August 9, 1945 (as part of the promise they made to America). I would've waited to see if Japan would surrender in the wake of this Russian intervention. I would've waited until Japan believed all hope in China was lost.
I would've waited until the sea blockade forced the majority of the starving Japanese people and the nervous Japanese cabinet to end the war (this is what Fleet Admiral Chester W. Nimitz suggested to President Truman). I would've given a public message to the Japanese nation saying that the Japanese Emperor will not be tried as a war criminal and will continue to rule the country after the war (this is what General Douglas MacArthur wanted Truman to do).
All these possibilities would've saved American lives, saved Japanese lives, given America a good image, and more importantly, ended World War II in a civilized manner.
Cause Japan didn't want to surrender. The war had already coast millions of lives and millions of dollars, and with Germany defeated, the war needed to come to an end immediatelly. Germany surrendered on May 8th 1945, Japan refused to surrender till August 9th of the same year and after the Nuclear Attacks of Hiroshima and Nagazaki 6th and 8th of August 1945.
The United States warned the Japanese authorities that they had Atomic bombs but Emperor Hiroito was just too stuborn to accept that he had lost the war.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.