Short Answer 
In 1945, following Germany’s surrender, the Allies shifted focus to the Pacific as Japan refused to surrender despite significant damage. Japan’s leadership rejected the Potsdam Declaration, prompting the US to prepare for a potential invasion, while facing challenges with resource allocation yet maintaining readiness for military action.
Step 1: Assessing the Global Context
In the spring and summer of 1945, the global landscape dramatically shifted after Germany’s surrender in July and the conclusion of the European war. This transition allowed the Allies to reallocate their resources, primarily focusing on the Pacific front against Japan. The necessity of this shift was critical for the United States as they aimed to deal with the ongoing threat posed by Japan.
Step 2: Understanding Japan’s Stance
Despite suffering significant damage from continuous bombing, Japan was still refusing to surrender. The Japanese leadership did not accept the Allies’ Potsdam Declaration, which outlined the terms for their surrender. Their reluctance to capitulate indicated that the only solution left for the Allies seemed to be a full-scale invasion to secure a unconditional surrender.
Step 3: Evaluating Military Resource Dynamics
While Japan was facing enormous losses, they were also attempting to rearm and posed a continued threat. The United States, although engaging heavily in air strikes, faced limitations in military resources. The other factors indicated that the US was statistically prepared to carry out an invasion, contradicting claims of stretched resources, thus shaping the decisions made by Truman during this critical period.