Which 1720 speculative collapse is associated with Britain's South Sea Company?

The 1720 speculative collapse associated with Britain's South Sea Company was the South Sea Bubble.

The South Sea Company received a government-backed monopoly over trade with Spanish South America, although its actual trading prospects were far more limited than many investors believed. Its shares rose dramatically in 1720 as promoters encouraged speculation and investors expected immense profits.

The boom collapsed later that year. As confidence weakened, the share price fell sharply, ruining many investors and creating a political scandal in Britain. The episode also involved complicated government debt arrangements, because the company took on public debt in exchange for shares and hoped that future profits would justify its valuation.

The same year saw another major speculative collapse, the Mississippi Bubble in France, connected with John Law's financial system. The two events are often discussed together, but they were separate schemes. South Sea Bubble is therefore the specific name for the British episode, not a general label for every 1720 financial disaster.