The stock market crash of October 1929 signaled the end of the "Roaring Twenties" and the beginning of the Great Depression. This was the second day of the big drop, known as "Black Tuesday," which began one day earlier and occupies the next spot on this list. 3.) Oct. 28, 1929 (-38.33, -12.82%)

Experts say the U.S. could be on the brink of a devastating market collapse like the 1987 crash, after President Donald Trump's tariff hikes.

Black Monday is the term used for Oct. 19, 1987 — a day when the U.S. stock market suffered its largest single-day percentage loss ever. The Dow Jones Industrial Average dropped a staggering 22.6 percent in one trading session.