In the early 19th Century agriculture began to change so fast and so many new products and technologies were being introduced that farmers need one place to see them all. That was the origin of the Exposition.
Over that century expos expanded to include a wide range of technologies including architecture and home products. By the end of the 19th Century we had national expos that displayed the technology of entire nations and we had religious expos that introduced new religions. Buddhism, Hinduism and Bahai came to America with the great religious expo of 1893.
By the end of the 19th Century the word fair and expo became interchangeable.
Have you noticed that by the 1960's the fairs and expos were becoming quite irrelevant and boring. Merely show cases for national competition.
My key insight is that today, fairs and expos, which had gone from technology demonstrations to national technology competitions have now migrated to Olympics. Olympics are the new national competitive scenes.