How did the superpowers react to the 2 chinas?

When the Chinese Civil War began (ending up with a Marxist regime on the mainland) there were no super powers. However, Japan took advantage of the situation by invading China.

At the end of World War II both the United States and the Union of Soviet Socialist Republics were too self-involved with social change to pay a lot of attention to China which traditionally has been an isolationist state, to begin.