First, because the bomb was completely unnecessary, Japan had surrendered and was simply trying to keep their emperor not hanged as a war criminal (which he was)
And second, because what was intended by Truman, fiercely anti-Russian, was to stop Russia in the Pacific, before they conquer more land, as Russia went to war in compliance with agreements reached at Yalta
|Yalta Conference February 1945|
The splendid book of Alexander Werth "Russia at war", London 1962, explain it very well.
When Churchill ( a strong anti-Russian ) knew of the success of the experiment with the atomic bomb in New Mexico, the first thought was that
" We shoud not need the Russians. The end of the Japonese war no longer depended on the pouring in of their armies...We had no need to ask favours of them... I minuted to Mr Eden. "It´s quite clear that the United States do not at the present time desire Russian participation in the war against Japan."
There was no doubt, he wrote, that the bomb would be used."
Before the Hiroshima´s bomb ( August 6, 1945 ) the Japonese sought Russian mediation in their desire to end the war with the USA and britain, several times.Even the Emperor decided to send Prince Konoye to Moscow in July 12, but Russia in compliance with the agreements with its allies and preparing to go to Postdam´s Conference, not accepted.
|Postdam Conference July-August 1945|
The Western official historiology says Japan did not accept, but according to Japanese sources virtually accepted but asking for some clarifications, according to the book of A. Werth mentioned indicates "...that the Japanese response to Ultimatum was misunderstood, or more probablemete deliberately mistranslated by some US officials, translating "no comment pending further information" for "we're ignoring the ultimatum," the word meaning mokusatsu ither "ignoring" or "no comment", acording to the contest."
"Japan was on the point of surrendering at the time of the Postdam Ultimatum, and merely wanted assurances concerning the status of the Emperor - the very question Ambassador Sato put to Molotov ( Russian minister ) on August 2, four days before the Hiroshima bomb"
How unnecesary it was to drop the atom bomb is shown by Major-General J.F.C Fuller in the Second World War ( London 1948), p 395: " On the 10th a broadcast from Tokyo announced the acceptance of the Postdam Ultimatum" with the understanding that does not comprise any demand which prejudices the prerogatives of the Emperor as a sovereign ruler". On the following day the Allies replied : " From the moment of surrender the authority of the Emperor... shall be subject to the Supreme Commander of teh Allied Powers". ( In other words there was no question of hanging the Emperar as a war criminal )."
Other confirmation of the USA intentions was exposed when in 1960 asked Mr Byrnes ( Secretary of State 1945-47 )wheter there was any urgency to end the war in the Pacific before the Russians become too deeply involved, Mr Byrnes replied : " There certainly was on my part. We wanted to get trough with the Japaneses phase of the war before the Russians came in ".
Truman's arrogance because he knew that it was the only country that had the atomic bomb was noted immediately :
"... On August 16 Truman declared that unlike Germany, Japan would not divided into occupation zones. Truman firmly rejected the Russian proposal that the Japaneses surrender to Russian troops in northern Hokkaido; nor were the Russians to take any part whatsoever in the occupation of Japan. Truman went even further: on August 18 he asked that the Russians let the Americans use one of the Kurile Islands as an air base, a proposal that Stalin rejected with a great show of indignation ".(1)
This superb and miserly attitude contracts with the generosity of allowing the Russians to divide the conquered Berlin ( exclusively with Russian blood ) into four parts.
|1Includes only losses in ground combat.|
In summary :
1. USA with the agreement of England wanted to explode the bomb to demonstrate his power and stop Russia (they sought help from her in Yalta) and not have to share the loot.
2. For this purpose ignored acceptance of surrender by Japan.
3. The second atomic bomb was even more unnecessary than the first.
(1) Russia at war . Alexander Werth ( london 1964 ) pp 1043.