Staged to celebrate the completion of the Panama Canal, and drawing over 19 million visitors in only nine months, the Pan-Pacific International Expo rose like a literal jewel from the ashes of San Francisco's 1906 Earthquake and Fire.
A Century of Progress International Exposition was held in Chicago, Illinois from 1933 to 1934 to celebrate the city's centennial. The theme of the fair was technological innovation. Its motto was "Science Finds, Industry Applies, Man Conforms".
The 1939-40 New York World's Fair, located on the current site of Flushing Meadows-Corona Park, was one of the largest world's fairs of all time. The fair ran for two seasons and over 44 million people attended.
The Golden Gate International Exposition was held in San Francisco, California to celebrate the opening of the San Francisco-Oakland Bay Bridge and the Golden Gate Bridge. The exposition's first season ran from February 18, 1939 through October 29, 1939 and its second season was from May 25, 1940 through September 29, 1940.
The 1964/1965 New York World’s Fair, located on the current site of Flushing Meadows-Corona Park. The fair ran for two seasons and took place without sanctioning from the Bureau of International Expositions.
Expo 67 was held in Montreal, Quebec, Canada from April 27 to October 29, 1967. It was considered to be the most successful World's Fair of the 20th century, with over 50 million visitors and 62 nations participating.
I believe the BIE rules provide for postponement or extension of a world's fair based on Acts of God or labor disputes. I did an article for Ed Orth's publication Expo Info back in the late 60s or early 70s and wrote to the BIE to access information. Based on the data they provided me at the time, the 1937 Paris Exhibition was offered a chance to extend their run beyond the usual 6 month period based on floods and labor strikes that delayed the opening of several pavilions beyond the fair's opening date in May of 1937. The US Pavilion wasn't officially opened until July. The French government wisely decided to decline the offer due to the mounting threat of war.
No, not that ET, the Eiffel Tower!
Per Encyclopaedia Britannica, the Eiffel Tower was inaugurated on this date in 1889.
As most here know, the critics then were as short-sighted as some at later Expositions, but we are glad they didn't have their way and it was left in place.