William McKinley entered the U.S. House of Representatives in 1876 and was there for 12 of the next 14 years. He was associated with high tariffs, for he believed that such tariffs protected U.S. industry from foreign competition and benefited all segments of society. Losing the race for Speaker of the House in 1889, he became chairman of the powerful Ways and Means Committee. After losing his House seat in 1890, he won the governorship of Ohio the following year.

When he left that office in 1894, he was a front-runner for the 1896 Republican presidential nomination. McKinley won with the largest winning margin in the popular vote since Grant. As president, he dealt primarily with foreign policy. When Spain would not withdraw from Cuba, after attempting to suppress a long-standing revolt attempt, the Spanish-American War ensued. When the war ended in August 1898, the United States had become a world power.

As a result of the war, the United States occupied Cuba until its independence in 1902; and, acquired Puerto Rico and the Philippines. In the Philippines, the U.S. Army dealt with a native revolt while William Howard Taft was establishing a civilian government. McKinley was elected to a second term in 1900, with Theodore Roosevelt as vice president. On September 5, 1901, speaking at the Pan-American Exposition at Buffalo, NY, he said, "Isolation is no longer possible or desirable. The period of exclusiveness is past." The next day he was shot and died eight days later.