The document discusses America's expansion overseas in the late 19th century following the closing of the western frontier. It explores the forces pushing for overseas expansion, including commercial interests in new markets and raw materials, strategic military interests, and beliefs in cultural superiority. The Spanish-American War of 1898 resulted in the U.S. acquiring Puerto Rico, Guam, and the Philippines. This raised debates around U.S. imperialism and whether territorial expansion abroad violated principles of self-government and democracy.