Late to the party

History.com has this for 8 August:

On 8 August 1945, the Soviet Union officially declared war on Japan, pouring more than one million Soviet soldiers into Japanese-occupied Manchuria (map) in northeastern China, taking on the seven-hundred-thousand-strong Japanese army.
The dropping of the bomb on Hiroshima by the Americans did not have the effect intended: unconditional surrender by Japan. Half of the Japanese inner Cabinet, called the Supreme War Direction Council, refused to surrender unless guarantees about Japan’s future were given by the Allies, especially regarding the position of the Emperor, Hirohito. The only Japanese civilians who even knew what happened at Hiroshima were either dead or suffering terribly.
Japan had not been too worried about the Soviet Union, who were busy with the Germans on the Eastern front. The Japanese army went so far as to believe that they would not have to engage a Soviet attack until the spring of 1946. But the Soviets surprised them with their invasion of Manchuria, an assault so strong (of the 850 Japanese soldiers engaged at Pingyanchen, 650 were killed or wounded within the first two days of fighting) that Emperor Hirohito began to plead with his War Council to reconsider surrender. The recalcitrant members began to waver.

Rico says that's why we bombed Nagasaki...