In 1851 the Great Exhibition in the Crystal Palace started the boom in World's Fairs as "Great Britain made clear to the world its role as industrial leader," according to Civilization in the West. Expo 2010 Shanghai China is pretty much like that, with the nations of the world putting their best food forward to impress, with pavilions that range from the good, the bad, and the really ugly.
But why? What is the function of an expo? Historically, they were expressions of power and influence, usually by the most important country of the time. Exhibitors came from all over the world to show their wares, their culture, to curry favour with the biggest market in the world.