In august 1945, the primary reason the united states dropped a second atomic bomb on japan was because

The reason why the US dropped a second atomic bomb on Japan was because they refused to unconditionally surrender. The goal in using the first atomic bomb was to get the Japanese to surrender and agreed to the terms laid out in the Potsdam Conference. However, the Japanese refused to surrender, causing the US to use the second bomb. After this bombing, the Japanese finally agreed to an unconditional surrender.