The Pan-American Exposition was a World's Fair held in Buffalo, New York, United States, from May 1 through November 2, 1901. The fair occupied 350 acres (0.55 sq mi) of land on the western edge of what is now Delaware Park, extending from Delaware Avenue to Elmwood Avenue and northward to Great Arrow Avenue. It is remembered today primarily for being the location of the assassination of United States President William McKinley at the Temple of Music on September 6, 1901. The exposition was illuminated at night. Thomas A. Edison, Inc. filmed it during the day and a pan of it at night.

Leon Frank Czolgosz ( CHOW-gawsh; May 5, 1873 – October 29, 1901) was an American steelworker and anarchist known for the assassination of President William McKinley, whom he shot on September 6, 1901, in Buffalo, New York. The president died on September 14 after his wound became infected. Caught in the act, Czolgosz was quickly tried, convicted, and executed seven weeks later on October 29, 1901.

While some American anarchists described his action as inevitable, motivated by what they saw as the country's brutal social conditions, others condemned Czolgosz for hindering the movement's goals by damaging its public perception.