Final answer:
The Japanese Imperial government did not surrender prior to the atomic bombings due to a combination of hoping to negotiate peace, leadership changes, and the desire to avoid unconditional surrender potentially implicating the emperor in war crimes. The eventual use of nuclear weapons and the Soviet's entry into the war were decisive in Japan agreeing to unconditional surrender.
Step-by-step explanation:
Despite Japan's shattered sea and air power by the end of 1944, the Imperial government did not surrender because of several factors. These included a reshuffling of power within the Japanese leadership, with Prime Minister Hideki Tojo resigning over failed strategies. Furthermore, Japan's leadership underestimated the resolve of the United States and hoped to negotiate terms rather than accept an unconditional surrender. Hopes were pinned on the Soviet Union to mediate, but after atomic bombs were dropped on Hiroshima and Nagasaki and with the Soviet Union declaring war on Japan, Emperor Hirohito intervened and accepted an unconditional surrender.
The Japanese leadership's refusal to surrender stemmed partially from their belief that they could still negotiate terms and partly from the fear of the emperor being tried for war crimes if they accepted unconditional surrender. The prospect of a costly invasion of Japan, estimated to result in hundreds of thousands of American casualties, weighed heavily on the decision to use nuclear weapons. The use of atomic bombs, devastating conventional bombings, and the Soviet Union's entry into the war were critical in convincing the Japanese leadership to end the conflict.