The story
The expression Chinese Wall comes from the Great Wall of China and became a metaphor of barriers, known to go back to the United States stock market crash of 1929. The U.S. government saw the need to maintain separation (or an information barrier) between investment bankers and brokerage firms, to limit the conflict of interest between the two. The first use of Chinese Wall in the general context of keeping confidentiality is unclear.
Etymology from Wiktionary, CC BY-SA 4.0.