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. In many ways, westward expansion in the nineteenth century foreshadowed international expansion. The conquest of the Indians reflected a broader imperialistic impulse within the country. Arguments based on racial superiority and the nation’s duty to expand became justifications for expansion in North America and overseas. By the end of the nineteenth century, sweeping economic, cultural, and social changes led many in the United States 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, U.S. officials led the nation in a burst of overseas expansion from 1898 to 1904, in which 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.