Over the course of American history, and particularly in the 20th Century when America assumed a major role in the world, there have been many arguments about what constitutes the ideal approach to U.S. foreign policy.
The 20th Century began with a period of American imperialism borne out of a sense of obligation to people in the underdeveloped world and spurred, in the case of the Spanish-American war, by humanitarian passions that were excited by yellow journalism. Woodrow Wilson introduced a foreign policy concept that stressed universal principles, such as national self-determination and making the world safe for democracy. "Wilsonianism" has appeared in other guises since then, most notably in George W. Bush's "neoconservative Wilsonian" efforts to remake Iraq and Afghanistan into democracies.
These initiatives are associated with a school of thought known as "idealism" and sometimes "liberal internationalism." They have encountered resistance from another school of thought, called "realism," which is associated with an impulse toward realpolitik - i.e., emphasizing that policy should be guided exclusively by vital national interests and not political ideals or moral crusades. This school has been traditionally associated with figures like Hans Morgenthau and Henry Kissinger.