(FORTUNE Small Business) – It was a wondrous place and a heady time, the great Exposition of 1904. It was the Meet Me in St. Louis fair, where, as Judy Garland would one day sing, "Don't tell me the lights are shining any place but there." And on the grounds were a few legendary (if now anonymous) entrepreneurs who changed the flavor of American summers. An ice cream vendor, running out of bowls, grabbed some waffles from another vendor and made the first ice cream cones. Someone trying to sell hot tea on a steamy day tossed in some ice: voila! Iced tea. A sausage cooker put his wares on a bun and called it a hot dog.

For more than a century, the biggest display at the world's fairs was the can-do American spirit itself. Run mostly by civic boosters allied with big business, world's fairs were often a distraction from economic woes. But they were utopian and forward-looking, helping to inspire generations to trust in progress and reach for the new. Their very success helped spur their own demise.

"Going to the fair" is a concept as old as commerce. But the first extravaganza of the kind we recognize came in the U.S. in 1853 (earlier in Britain), when some New York City businessmen built a glass-and-steel "palace of crystal" on a tract of land that is now in midtown Manhattan. Coming on the heels of an economic panic, the fair, with its displays of newfangled reapers and Matthew Brady's photographs, suggested that America was at the vanguard. World's fairs became the rage for cities trying to prove their might--Philadelphia in 1876; Paris in 1889; Buffalo, Chicago, and San Francisco in the early 1900s. Another spate flourished in the 1930s, and a third during the Cold War. They "often came in response to economic and political upheaval," says historian Robert W. Rydell. "The 1933 fair was called 'A Century of Progress.' What optimism!"

The fairs were democratic ventures, open to anyone--at a price. In 1904, when $12 a week was a good salary, millions spent 50 cents to get into the St. Louis fair. You went to the fairs to be amazed and entertained and to see into the future. You gaped at the huge riding wheel made by George Washington Ferris in Chicago and at M. Eiffel's tower in Paris. The geniuses were often there in person: young Alexander Bell with his new telephone in 1876, Thomas Edison with his Kinetoscope in 1893, David Sarnoff with the television in 1939. And the utopian approach put pavilions from foreign lands, even those politically at odds, side by side.

That was the message behind the "Small World" pavilion Disney built for Pepsi-Cola at the 1964 fair. But that creation also heralded the decline. It became an anchor for Disneyland. Theme parks, with their own grand midways and corporate backing, became, in a sense, permanent world's fairs.

It's hard to imagine how world's fairs today could play their historic role. Innovations come so fast that as soon as one wows, another bows. And a visitor who can "instant message" her pen pal in Tibet isn't wowed as easily. World's fairs still exist, but they are more modest affairs. More than 51 million people came to New York in 1964; 13 million are expected at Expo 2000 in Hannover, Germany, this year. Nothing as revolutionary as a phone or TV will make its debut. Just a calm--maybe quaint--celebration of world culture.