This post first appeared on Today in Alternate History.
 
"We - the President of the United States, the President of the National Government of the Republic of China, and the Prime Minister of Great Britain, representing the hundreds of millions of our countrymen, have conferred and agree that Japan shall be given an opportunity to end this war. We call upon the government of Japan to proclaim now the unconditional surrender of all Japanese armed forces, and to provide proper and adequate assurances of their good faith in such action. The alternative for Japan is prompt and utter destruction." ~ OTL Potsdam Declaration
June 15, 1945 - Nationalist China is saved by Fat Boy
In early 1945, the progress of the Manhattan Project was rapidly accelerated by the strategic choice of Uranium Implosion over easier but inefficient impact detonation. This bold decision was taken despite many leading scientists expressing deep concern that the design was far too theoretical to implement.
The benefits soon became clear. Less than a fortnight after the fall of Berlin, one atomic weapons was ready for immediate deployment and enough uranium was available to rapidly build four more. This compressed timing of the deployment schedule was highly significant because the tentative plan had always been for the Soviets to declare war on Japan within three months of victory in Europe. With the Red Army occupying Eastern Europe, the Western Allies suddenly had an opportunity for victory on their own exclusive terms. 
Such an outcome would transform the post-war landscape, having profound 
affects not only for Japan, but for Mao Zedong's Communists also.
The
 detonation of the world's first atomic bomb would be a supreme 
expression of American authority. Although many other Allied nations 
might profit from an earlier victory over Japan, the main beneficiary 
would of course be US hegemony. In the long-term, history would draw a 
straight line from Admiral Perry's arrival in Tokyo Bay through Theodore
 Roosevelt's mediation of the Russo-Japanese War and onto VJ Day. 
Despite this contemporary perspective, explosive experts from the United
 Kingdom had played a major part in the breakthrough.  As a result of 
this decisive contribution, the UK would gain a third part of the 
arsenal and become the second atomic weapon-state.
The detonation
 of the "Fat Boy" device over the Japanese city of Hiroshima was 
insufficient to force the Supreme War Council to capitulate. However, 
the subsequent threat of further bombs - and critically the assurance 
that the Emperor could rule as a figurehead under Allied Occupation - 
was enough to swing Foreign Minister Togo into the peace camp. Despite 
the rising threat of insurrection, Japan would issue a declaration of 
unconditional surrender before the end of June.
There would be a 
very high price to be paid for victory. For example, Manchuria had been 
an independent nation prior to 1931. The Japanese Kwantung Army was 
undefeated in the field and many Japanese colonists in Manchuria had 
suddenly become stateless citizens. Moreover, it was improbable that the
 Soviets would fully accept this status quo even though the UN 
Security Council was stacked with capitalist victor powers. Once Eastern
 Europe was under control, the Soviets began to clandestinely 
support liberation movements across the Far East in a determined attempt
 to undo American influence. The  inevitable consequence was a huge 
commitment to post-war Asia. 
Many political analysts confidently
 predicted that Chiang Kai-shek's National Regime was doomed anyway. 
These unresolved concerns for the future would overshadow the peace 
settlement even though Britain, France, and the Netherlands would quickly
 move to reoccupy the territories in their Asian Empires. Of course, 
because the French and Dutch were not yet nuclear powers, they did not 
have the chance to threaten guerrilla armies with the atomic bomb. By 
the time that France had the capability to do so, the war in Indochina 
was already lost.
Author's Note:
In reality, the Manchurian 
Strategic Offensive Operation would set the stage for the Chinese Civil 
War and the triumph of Mao Zedong. President Truman would be accused of 
"losing China." In this scenario, we imagine the possibility of a 
region-wide Vietnam scenario.
