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South Sea Bubble 1720

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South Sea Bubble 1720

The South Sea Bubble stands apart from most market manias because it was not merely a spontaneous outbreak of investor enthusiasm—it was a government-sponsored scheme to convert national debt into company equity. When the South Sea Company's shares rose from £100 to over £1,000 in the spring and summer of 1720, they carried with them the implicit credibility of Parliament and the Crown. When the shares collapsed back below £100 by autumn, they took with them the savings of thousands of investors, the reputations of ministers, and several members of the government's inner circle.

Government debt and financial engineering​

Britain in the early eighteenth century carried an enormous debt burden from two decades of war. The South Sea Company, founded in 1711, offered a solution: it would assume the national debt in exchange for a monopoly on trade with Spanish South America—a monopoly that existed mostly on paper, since the Treaty of Utrecht granted only limited trading rights. The company's value, in other words, rested on future earnings that were highly speculative at best, and entirely fictitious at worst.

The machinery of promotion​

What transformed a dubious financial scheme into a national mania was a combination of insider dealing, bribery of key officials, and an aggressive campaign of investor recruitment. Company directors made secret share distributions to members of Parliament and royal ministers to ensure favorable legislation. Coffeehouse brokers spread optimistic rumors. The King himself accepted shares. By the spring of 1720, the rising price had become self-validating—each day's advance attracted new buyers who saw the price history as proof of the company's value.

Newton, the crowd, and the limits of genius​

The bubble's most instructive cameo belongs to Isaac Newton, who correctly sold his South Sea shares in April 1720 for a profit, watched the price continue to rise, bought back in at a far higher price, and lost an estimated £20,000 when the crash came. His reported remark—that he could calculate the motions of heavenly bodies but not the madness of people—captures the central insight of behavioral finance: intelligence and analytical ability do not immunize an investor against the emotional pull of a rising market.

Aftermath and reform​

The parliamentary investigation that followed the crash revealed systematic corruption at the highest levels of government. Several directors were imprisoned and their estates confiscated. The Bubble Act of 1720, passed during the mania, restricted the formation of joint-stock companies without royal charter—an overcorrection that hampered legitimate business formation for over a century. The episode established the template for post-crisis regulatory overreach: rules written in the heat of collapse that address the specific instruments of the last crisis rather than the underlying dynamics that will power the next one.

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