St Louis World's Fair

The St. Louis World's Fair was also known as the Louisiana Purchase Exposition.  It was originally scheduled for the centennial 1903, but was moved back a year to allow more countries and states to participate.  43 of the 45 states at the time participated.  As did many territories, including new territories as a result of the Spanish American war such as the Philippines and Guam.  62 foreign nations participated.  The fair had almost 20 million visitors.
The original land used for the fair is now part of Washington University and Forest Park.  This was the biggest fair up to that time, with 1500 buildings, 1200 acres and 45 miles of roads and trails.  They said you couldn't see it all in a week.
Noted exhibits included Geronimo, ragtime music and Scot Joplin, Helen Keller, 24, lectured, John Phillip Sousa and his band played.  T.S. Elliot also visited.  Many foods were popularized including the waffle cone, peanut butter, iced tea, cotton candy, and even to an extent hot dogs and hamburgers were popularized.
The 1904 Summer Olympic Games were held as part of the fair and went on for a drawn out period.  However they were overshadowed by the fair.  Source Wikipedia
The fair is the backdrop to the 1944 movie, "Meet me in St. Louis."
http://mmboebillywardle.blogspot.com/2013/12/christmas-musical-movie-review-meet-me.html
The stamps show Robert Livingston, French negotiator, Thomas Jefferson U.S. President who ordered the Lewis and Clark expedition, James Monroe U.S. negotiator, William McKinley proponent of the exposition, and a map of the Louisiana Purchase.  They were issued April 30, 1904.