At the dawn of the twentieth century, America’s rising economic supremacy was the subject of frequent commentary in both Europe and the United States. The French economist Louis Bosc warned that America would soon dominate the “universe.” Brooks Adams, grandson of John Quincy Adams, more admiringly commented on the “velocity and proportions” of the new “American supremacy,” declaring the United States “a gigantic and growing empire.” And in 1902, the English writer W. T. Stead, impressed by Americans’ “exuberant energies,” published a short volume with the arresting title, The Americanisation of the World, or the Trend of the Twentieth Century, predicting that the United States would soon emerge as “the greatest of world powers.”

The United States had, indeed, emerged as a formidable empire by 1900. The conquest of Hawaii in 1893 expanded its territory halfway across the Pacific. The colonization of the Philippines and Puerto Rico after the Spanish-American War, along with the acquisition of Guam and American Samoa and in 1917 the Virgin Islands, added more than 7 million new people over whom the nation ruled. Yet the country’s overseas territorial holdings remained small compared to those of Britain, France, and Germany. In 1900, Great Britain ruled over more than 300 million people in possessions scattered across the globe, and France had nearly 50 million subjects in Asia and Africa. America’s empire differed significantly from those of European countries.

On the North American continent, the United States had vastly expanded since its founding. In the first half of the nineteenth century, American Indian expropriation, land purchased from European empires, and the war with Mexico more than tripled the size of its territory. By the early twentieth century, America had emerged as a continent-spanning nation with a growing population and abundant mineral and agricultural resources that helped drive its extraordinary economic growth. By 1913, the United States produced 65 percent of the world’s petroleum, 56 percent of the world’s copper, 39 percent of its coal, and 36 percent of its iron ore. By 1914, it produced more than one-third of the world’s manufactured goods. Although Britain still dominated world banking and the British pound remained the major currency of international trade, the United States had become the leading industrial power. Europeans complained of an “American invasion” of steel, oil, agricultural equipment, and consumer goods and many feared American products and culture would overwhelm them. “What are the chief new features of London life?” one British writer asked in 1901. “They are the telephone, the portable camera, the phonograph, the electric street car, the automobile, the typewriter. . . . In every one of these the American maker is supreme.”

The fierce economic competition Europe faced from the United States intensified European countries’ quest for overseas colonial control. With its own vast territory, the United States, however, was more interested in ensuring a favorable economic climate for American goods and trade abroad. America’s economic supremacy, W. T. Stead remarked, was grounded in the “single-minded commitment to the pursuit of wealth.” By the dawn of the twentieth century, its economic industries and corporate energies would lead the United States to promote its interests through newly energetic involvement in the affairs of other nations. As Brooks Adams wrote, the nation “must be brought into competition with rivals at the ends of the earth.” America’s influence was growing throughout the world.

America’s burgeoning connections with the outside world led to increasing military and political involvement. In the two decades after 1900, many of the basic principles that would guide American foreign policy for the rest of the century were formulated. The “open door”—the free flow of trade, investment, information, and culture—emerged as a key principle of American foreign relations. “Since the manufacturer insists on having the world as a market,” wrote Woodrow Wilson, “the flag of his nation must follow him and the doors of nations which are closed against him must be battered down.”

Americans in the twentieth century often discussed foreign policy in the language of freedom. At least in rhetoric, the United States ventured abroad—including intervening militarily in the affairs of other nations—not to pursue strategic goals or to enhance American economic interests but to promote liberty and democracy. A supreme faith in America’s historic destiny and in the righteousness of its ideals enabled the country’s leaders to think of the United States simultaneously as an emerging great power and as the worldwide embodiment of freedom.

More than any other individual, Woodrow Wilson articulated this vision of America’s relationship to the rest of the world. His foreign policy, called by historians liberal internationalism, rested on the conviction that economic and political progress went hand in hand. Thus, greater worldwide freedom would follow inevitably from increased American investment and trade abroad. Frequently during the twentieth century, this conviction would serve as a mask for American power and self-interest. It would also inspire sincere efforts to bring freedom to other peoples. In either case, liberal internationalism represented a shift from the nineteenth-century tradition of promoting freedom primarily by example, to active intervention to remake the world in the American image.

American involvement in World War I provided the first great test of Wilson’s belief that American power could “make the world safe for democracy.” Most Progressives embraced the country’s participation in the war, believing that the United States could help to spread Progressive values throughout the world. The government quickly came to view critics of American involvement not simply as citizens with a different set of opinions but as enemies of the very ideas of democracy and freedom. As a result, the war produced one of the most sweeping repressions of the right to dissent in all of American history. Rather than bringing Progressivism to other peoples, the war destroyed it at home.