In 1901, President William McKinley was assassinated by Leon Czolgosz, a Polish-American anarchist, while making a speech at the Pan-American Exposition in Buffalo, New York.

Czolgosz had become radicalized by reading about the assassination of King Umberto I of Italy and other anarchist attacks, and he believed that the assassination of a political leader would bring about social change. On September 6, 1901, he approached McKinley at the exposition and shot him twice with a revolver. McKinley died a few days later, and Czolgosz was quickly arrested, tried, and sentenced to death. He was electrocuted on October 29, 1901. The assassination of President McKinley was a significant event in United States history and had significant political consequences.