America's commitment to free capital markets, the rule of law and price stability confer credibility on the dollar as a store of value. But American spending habits have undermined the dollar's reputation, with excess supply of the dollar on world markets depressing its price.

In April this year, the euro's exchange rate against the dollar reached an all-time high, and central banks have increased the euro share of their international reserves. Is the dollar about to lose the crown of world finance to the euro?

History suggests otherwise, despite the vulnerability of the dollar.

American financial supremacy in the 21st century resembles Britain's position in world finance a century ago. Before the outbreak of World War I in August 1914, the pound sterling served as the currency of choice for international transactions, just as the dollar does today, and the world's borrowers visited the City of London to raise capital.

British economist John Maynard Keynes worried that countries would not use sterling to settle trading balances with one another if it were not viewed as a reliable store of value. The 'future position of the City of London', according to him, depended on sterling continuing to serve the business world as the equivalent of gold. Britain maintained sterling's convertibility into gold at the outbreak of the Great War to preserve its credibility as the international medium of exchange.

The dollar could not challenge sterling's role as the world's currency without matching its reputation. But then Treasury Secretary William G. McAdoo secured American financial honour in August 1914 by remaining true to gold while everyone else, except for the British, abandoned their obligations. Despite the dollar's instant credibility, however, it took more than a decade for America's currency to match Britain's as an international medium of exchange. Payment habits melt at a glacier's pace.

Britain's transformation from international creditor to international debtor during the Great War gave the dollar a second wind in its battle with sterling. The British were forced to abandon gold convertibility in April 1919. In April 1925, Britain returned to the gold standard, but the sterling had already suffered irreparable damage.

The experience of 1914 implies that a credible alternative can replace an entrenched world currency, especially after an unfavourable balance of trade has weakened it. But even then, dethroning the reigning king of international exchange takes time.

Recent experience with the euro as an official reserve asset is instructive. Between 2000 and 2005, the dollar lost more than 25 per cent of its value against the euro. Meanwhile, the fraction of international reserves held in euros grew from 18 per cent to 24 per cent, and the dollar's share dropped from 71 per cent to 66 per cent. In short, the euro has clearly made some headway during this period of US balance of payment deficits, but this reflects an evolutionary decline in the dollar's dominance, not a revolutionary regime shift.

What might trigger a fatal run on the dollar in world markets? While a broad and abrupt sell-off by major foreign holders of dollars - for example, China - appears unlikely, a cataclysmic event, similar to the outbreak of the Great War in 1914, could prompt a search for a new international medium of exchange.

In the modern era of automated payments, the upheaval might come from a terrorist attack that undermines the computerised transfer facilities of the world's banking system. A catastrophic loss of electronic records could surely destroy the credibility of the dollar as the international medium of exchange.

But exactly what would replace the dollar under such circumstances remains an open question. After all, a loss of computer records would make the euro equally suspect. Perhaps gold, a store of value impervious to physical distortion, could make a comeback. Of course, one can only hope that such a scenario remains pure conjecture.

William L. Silber is a professor of finance and economics at New York University's Stern School of Business and author of When Washington Shut Down Wall Street: The Great Financial Crisis Of 1914 and The Origins Of America's Monetary Supremacy.

Copyright: Project Syndicate, 2007. www.project-syndicate.org