The 1720 speculative bubble involving soaring and collapsing shares in a British trading company was the South Sea Bubble.
The South Sea Company received a government-backed monopoly over British trade with parts of Spanish America, although its realistic trading opportunities were far more limited than many investors believed. In 1720, the company promoted a plan to convert government debt into company shares. Prices rose dramatically as investors expected enormous profits.
Shares climbed from about £128 in January to nearly £1,000 in August before confidence broke. The price then collapsed, ruining many investors and causing a political scandal. Parliament investigated the episode, and several directors were accused of corruption or improper dealings.
The South Sea Bubble occurred alongside John Law's Mississippi Bubble in France, but they were separate schemes. It also predates modern stock exchanges and should not be described as a conventional twentieth-century market crash. The episode became a lasting example of speculation, leverage, promotional hype, and herd behavior.