[scarmig]

> We didn't understand that the Sino-Soviet split had happened until decades later, and still thought that China and Russia formed a united communist bloc well into the 80s

This is not true. See e.g. the 13 August 1969 Presidential briefing:

https://www.cia.gov/library/readingroom/docs/DOC_0005976931....

Choice quotes:

"The potential for war between them clearly exists."

"A climate of high tension, marked by periodic border clashes, is likely."

"Peking, which appears to view the USSR as its most immediate enemy, will face stiff competition from the Soviets in attempting to expand its influence in Asia."

The USA actually held discussions with the USSR to bomb China's nuclear missile facilities. Moreover, this knowledge aiding in reaching rapprochement with China in 1972.