The Preparedness Movement was a campaign led by former Chief of Staff of the U.S. Army, Leonard Wood, and former President Theodore Roosevelt to strengthen the U.S. military after the outbreak of World War I. Wood advocated a summer training school for reserve officers to be held in Plattsburgh, New York.

The movement was at first opposed by President Woodrow Wilson, who believed the United States should be in a position of neutrality in order to broker a compromise peace in Europe. Several organizations were formed around the Preparedness Movement and held parades and organized opposition to Wilson's policies. After the Lusitania was sunk by German U-boats on May 7, 1915, and Pancho Villa launched his raid against Columbus, New Mexico, Wilson's attitude changed. The United States Congress passed the National Defense Act of 1916 in June 1916 to authorize an increase in the size of the U.S. Army from 100,000 men in 1916 to 200,000 on active duty and 400,000 in the U.S. National Guard, by 1921. It also padded a large long-term increase in the U.S. Navy.