U.S. President William McKinley dies after being mortally wounded on September 6 by anarchist Leon Czolgosz and is succeeded by Vice President Theodore Roosevelt.

William McKinley was the 25th president of the United States, serving from 1897 until his assassination in 1901. A member of the Republican Party, he led a realignment that made Republicans largely dominant in the industrial states and nationwide for decades. McKinley successfully led the U.S. in the Spanish–American War and oversaw a period of American expansionism, with the annexations of Hawaii, Puerto Rico, Guam, the Philippines, and American Samoa.

William McKinley, the 25th president of the United States, was shot on the grounds of the Pan-American Exposition in the Temple of Music in Buffalo, New York, on September 6, 1901, six months into his second term. He was shaking hands with the public when an anarchist, Leon Czolgosz, shot him twice in the abdomen. McKinley died on September 14 of gangrene caused by the wounds. He was the third American president to be assassinated, following Abraham Lincoln in 1865 and James A. Garfield in 1881.

September 6 is the 249th day of the year in the Gregorian calendar; 116 days remain until the end of the year.

Leon Frank Czolgosz was an American wireworker and anarchist who shot United States president William McKinley on September 6, 1901, in Buffalo, New York. McKinley died on September 14 after his wound became infected. Caught in the act, Czolgosz was tried, convicted, and executed by the State of New York seven weeks later on October 29, 1901.

Theodore Roosevelt Jr., also known as Teddy or T. R., was the 26th president of the United States, serving from 1901 to 1909. Roosevelt previously was involved in New York politics, including serving as the state's 33rd governor for two years. He served as the 25th vice president under President William McKinley for six months in 1901, assuming the presidency after McKinley's assassination. As president, Roosevelt emerged as a leader of the Republican Party and became a driving force for anti-trust and Progressive Era policies.