Black Monday is the name commonly attached to the global, sudden and largely unexpected stock market crash on October 19, 1987. In Australia and New Zealand it is called Black Tuesday because of time zone differences from the United States.
All the twenty-three major world markets had sharp declines in October 1987. Under the United States dollar, eight markets declined by 20% to 29%, three by 30% to 39% (Malaysia, Mexico and New Zealand and another three by 40% or more (Australia, Hong Kong and Singapore).
This Black Monday was called the worst in history at the time.
Circuit breakers were put up for stopping another 1987-like crash. It took two years for the Dow Jones to recover.