> Regulators put the first circuit breakers in place following the market crash of October 19th 1987, when the Dow Jones Industrial Average (DJIA) shed 508 points (22.6%) in a single day. The crash, which began in Hong Kong and soon affected markets worldwide, came to be known as Black Monday.
Well something was put into place after 1929...
> In 1933, the U.S. Congress passed the Glass–Steagall Act mandating a separation between commercial banks, which take deposits and extend loans, and investment banks, which underwrite, issue, and distribute stocks, bonds, and other securities.
It was repealed in 1999.
https://en.wikipedia.org/wiki/Aftermath_of_the_repeal_of_the...
I assume they have been tweaked since 1929, but they started with the crash back then.
Edit: someone else is claiming 1987 as the start. My memory says 1929. If this matters do your own research.