What is a world's fair or expo?
It is a large public exhibit that has its origins in the 1800s when world fairs originated in the French tradition of national exhibitions, a tradition that culminated with the French Industrial Expo of 1844 in Paris. This fair was soon followed by other national exhibitions all over Europe.
During the era of industrialization - from 1800 to the 1930s - world expos were especially focused on trade and were famous for the display of technological inventions. World expos brought together state-of-the-art science and technology from around the world. Inventions such as the telephone were first presented during this time.
The 1939 New York World’s Fair diverged from previous world's fair exhibits because it had a specific theme: "Building the World of Tomorrow." So from then on, technological innovations were no longer the primary focus, but world expos rather forecasted a better future for society. At the 1964-65 New York World’s Fair it was "Peace Through Understanding," and at the 1967 International and Universal Exposition in Montreal, the theme was "Man and His World." The fairs encouraged effective intercultural communication for the exchange of innovation.
Interesting side story/tidbit: The 1967 International and Universal Exposition in Montreal was promoted under the name Expo 67. Event organizers retired the term world's fair in favor of expo, and the Montreal Expos were named for the 1967 fair.
From Expo ’88 in Brisbane, onwards countries started to use world expositions more widely and more strongly as a platform to improve their national images through the use of national pavilions.
Today's world expos include elements of all three eras. They present new inventions, facilitate cultural exchange and are used for city, region and nation branding. The 2015 world expo is being held in Milan, Italy.