The United States became a modern imperial power relatively late. In the decades following the Civil War, the U.S. government concentrated most of its energies on settling the western territories, pushing Native Americans aside, and extracting the region’s resources. Unlike Europe, the United States possessed a sparsely inhabited frontier that would furnish land for its growing population, as well as raw materials and markets for its industries. By the end of the nineteenth century, however, sweeping economic, cultural, and social changes led many Americans to conclude that the time had come for the country to assert its power beyond its borders. Convinced of the argument for empire advanced by Mahan and other imperialists, American officials embraced an expansionist foreign policy. In a burst of overseas expansion from 1898 to 1904, the United States acquired Guam, Hawaii, the Philippines, and Puerto Rico; established a protectorate in Cuba; and exercised force to build a canal through Panama. These gains paved the way for subsequent U.S. intervention in Haiti, the Dominican Republic, and Nicaragua.