In many ways, Woodrow Wilson personified the belief in American exceptionalism. As Robert E. Osgood argues: "Wilson's national altruism … was an integral part of his temperament and his philosophy of life, inseparable from his personality." Wilson's idealism was firmly grounded in the belief that the United States was a nation set apart by its values and principles from the rest of the world. He believed strongly that the "force of America is the force of moral principle" and that the "idea of America is to serve humanity." Long before he became president, Wilson wrote of his conviction that the United States had a "plain destiny [to] serve [rather than] subdue the world." Later, as president, he would contend that this destiny to serve was the only possible motivation for American actions in the world. Wilson held that "morality not expediency" must be the guiding principle of all American policy. He applied this principle to the use of American military force. As Frederick Calhoun argues, Wilson "showed no aversion to fighting if the end justified the means." As Wilson stated, he believed that while other nations used force "for the oppression of mankind and their own aggrandizement," the United States would use force only "for the elevation of the spirit of the human race."
Wilson declared that "the United States will never again seek one additional foot of territory by conquest." Nevertheless, he frequently used military intervention in efforts to help other peoples become, in his opinion, more democratic and orderly. Wilson sent American troops into Mexico twice, to Haiti, the Dominican Republic, and Cuba, as well as maintaining the military "protection" of Nicaragua. He also intervened militarily twice in the Russian civil war. Wilson best expressed his attitude toward such interventions in 1914: "They say the Mexicans are not fitted for self-government and to this I reply that, when properly directed, there is no people not fitted for self-government." Wilson was a clear advocate of the missionary strand of American exceptionalism.
When Wilson finally made the decision to enter World War I in April 1917, he justified his action in highly idealistic terms that enabled the American people to come to regard the war as a crusade. Most famously, the determination to "make the world safe for democracy" was proclaimed by President Wilson as he asked Congress for a declaration of war against Germany. The United States, in keeping with its traditions, was joining the hostilities according to Wilson with nothing but the most benign intentions and a sense of a higher purpose. Portraying involvement in the conflict as a just cause in terms consistent with the belief in American exceptionalism was a direct and deliberate appeal to the public and a way to help silence opposition. It was also the only way that Wilson could assuage his own doubts about American involvement in the war. The rhetoric that accompanied intervention made it clear that the United States, in keeping with its strongest principles, was taking a stand against autocratic tyranny, much as it had against the British in the American Revolution and against the Spanish over Cuba. Wilson argued that a peaceful and harmonious postwar international order based on the principle of universal freedom and democracy, as enshrined in the U.S. Constitution, could not be established while autocratic imperialism sought dominance in Europe. Although legitimate political, economic, and strategic justifications for intervention existed, American involvement in World War I was thus justified and conducted in terms consistent with the missionary strand of the belief in American exceptionalism.