Economic nationalism tended to dominate U.S. foreign trade policy throughout the long 19th century, from the end of the American Revolution to the beginning of World War I, owing to a pervasive American sense of economic and geopolitical insecurity and American fear of hostile powers, especially the British but also the French and Spanish and even the Barbary States. Following the U.S. Civil War, leading U.S. protectionist politicians sought to curtail European trade policies and to create a U.S.-dominated customs union in the Western Hemisphere. American proponents of trade liberalization increasingly found themselves outnumbered in the halls of Congress, as the “American System” of economic nationalism grew in popularity alongside the perceived need for foreign markets. Protectionist advocates in the United States viewed the American System as a panacea that not only promised to provide the federal government with revenue but also to artificially insulate American infant industries from undue foreign-market competition through high protective tariffs and subsidies, and to retaliate against real and perceived threats to U.S. trade. Throughout this period, the United States itself underwent a great struggle over foreign trade policy. By the late 19th century, the era’s boom-and-bust global economic system led to a growing perception that the United States needed more access to foreign markets as an outlet for the country’s surplus goods and capital. But whether the United States would obtain foreign market access through free trade or through protectionism led to a great debate over the proper course of U.S. foreign trade policy. By the time that the United States acquired a colonial empire from the Spanish in 1898, this same debate over U.S. foreign trade policy had effectively merged into debates over the course of U.S. imperial expansion. The country’s more expansionist-minded economic nationalists came out on top. The overwhelming 1896 victory of William McKinley—the Republican party’s “Napoleon of Protection”—marked the beginning of substantial expansion of U.S. foreign trade through a mixture of protectionism and imperialism in the years leading up to World War I.