At the end of the Anti-Japanese War, after the Soviet troops occupied the Northeast, why didn't they take it and leave, but retreated?

The Soviet war ended in May. According to the agreement, in August in northeast China, against the Japanese. This is an agreement. Therefore, he dare not occupy it. Otherwise, the allies will not allow him.

Besides, don't really think that the Soviet Union has any good intentions. The decisive factor at that time was actually the atomic bomb dropped by the United States in Japan. Japan is frightened, and I wonder how many such weapons there are in the United States. Therefore, there are only ten forms for the Soviet Union to send troops to Northeast China. Another main function of their coming to the northeast is to dismantle a large number of facilities in the northeast. What is left to the China government is destruction.

Some historical knowledge is quite different from what we learned in school before.