What's an example of a black market?
One of the best-known black markets in American history was Prohibition, or the period from 1920 to 1933, when the manufacturing, transportation, and sale of alcohol was illegal.
Although alcohol was illegal during the time, drinking moved to hidden locations known as speakeasies, and alcohol was run by bootleggers. Prohibition enriched organized crime figures, including Al Capone, giving them further influence with businesses and political leaders, and they often bribed those figures with illegal alcohol.
By 1932, political leaders had recognized that Prohibition was a failure, and the prospect of increased tax revenue was appealing during the Great Depression. The 21st Amendment was passed, reversing the 18th Amendment, which had banned alcohol, and legal drinking was reinstated.