White House Biography
From the official White House site

The American President: William McKinley
Another finely detailed biography

William McKinley
Wikipedia bio of the president

William McKinley
Biography from the Internet Public Library

The Election of 1896
McKinley's first victory

The Spanish-American War
This war ended the 19th Century and began the 20th

The Election of 1900
McKinley's second victory

William Jennings Bryan
Powerful Populist politician who ran for president three times as a Democrat (and lost twice to McKinley)

The Assassination of President McKinley
The whole sordid story