Has American foreign policy been driven by a pragmatic approach to solving problems of national interest and security? Has American foreign policy been driven by a series of ideas? The popular answer is the ideas one because there’s so much evidence that is easily found.
For one thing, until very recent times, Americans were a religious people. Many still are. So, many discussions of public affairs—foreign and domestic–were couched in religious terms. Often, they presented the United States as an agent of the Divine, or discussed conflicts in terms of Good and Evil. President McKinley talked about America’s duty to “uplift and Christianize” the Filipinos. Abraham Lincoln’s Second Inaugural Address is explicitly religious.
For another thing, historians often take a published rationalization for doing something as the actual inspiration for doing that thing. In the case of the Westward movement, Thomas Jefferson proclaimed the desire to create an “Empire of Liberty” and John O’Sullivan announced America’s “Manifest Destiny.” In the case of engaging with the larger world, Alfred Thayer Mahan emphasized the “Influence of Sea Power Upon History,” and Woodrow Wilson justified American entry into the First World War as an effort to “make the world safe for democracy.”
Despite this eye-catching froth, most American policy has been driven by attempts to find pragmatic solutions to real problems. The truth is that Americans had been moving Westward in ever-growing numbers since they landed on the Eastern seaboard. High-flown talk didn’t make them go. The practical problems were how to fend off foreign competitors (France, Spain, Mexico, Britain) and how to dispossess the Native Americans. Similarly, by the dawn of the 20th Century, America’s economic development and population growth gave the United States an interest in world trade and made it a country to be reckoned with in international affairs.
The United States entered the First World War because Germany, more than Britain, threatened the principle of freedom of the seas and the idea of a world governed by law. The idealistic war aims came later. American isolationism in the Thirties ended with the unexpected fall of France in 1940, and the near-collapse of Britain. The real German danger to American security shifted military, diplomatic, and domestic political positions in a hurry. The United States adopted the policy of “containment” against the Soviet Union to secure America’s essential trading partners and military allies. Eisenhower adopted the strategy of “more bang for the buck” to keep down the size of the military budget. This prefigured his farewell address warning of a “military-industrial complex” that is with us yet.
This pragmatism didn’t always have a happy outcome. The George W. Bush administration made a correct analysis of the sources of terrorism in the Middle East: centuries of Ottoman and Arab bad government, not Western imperialism. Then it came up with a disastrously wrong solution: knock over a dictator, declare “democracy,” put up some big-box stores, and leave. You can’t make anything fool-proof. Fools are too inventive.
 Inspired by reading David Sanger, “Nation-Building’s Siren Song,” NYT Book Review, 1 January 2017.
 The tendency of writers and politicians to say things in print got a lot of these people shot in France after the Second World War. Meanwhile, bureaucrats and businessmen who had collaborated with the Germans went free. See: Peter Novick, The Resistance versus Vichy: The purge of collaborators in liberated France (1968).
 See: https://en.wikipedia.org/wiki/Abraham_Lincoln%27s_second_inaugural_address
 See: Ernest May The World War and American Isolation, 1914-1917 (1959); Ray S. Cline, Washington Command Post: The Operations Division (1951); John Lewis Gaddis, Strategies of Containment (1982).