This essay is based on the author's presentation at the Wachman Center's July 26-27, 2008 history institute, co-sponsored and hosted by the Cantigny First Division Foundation of the McCormick Tribune Foundation. For Europeans, World War I remains the epochal event of the twentieth century. For Americans, the war falls between two much larger and more emotive events in American history, the Civil War and World War II. Although the war did not result in destruction for Americans on the European scale, it nevertheless had deep and sometimes forgotten impacts on the United States. It led to fundamental, long-term changes in the way America and Americans relate to the outside world. On the American home front, the idea of intervening in a bloody and seemingly inconclusive European war for unclear gains generated tremendous controversy. Others believe that the mass movement of people across the nation, the shared military service of Americans (in segregated units) raised across the nation, and increased government standardization of the economy laid the groundwork for the emergence of a national mindset. The author concludes that World War I is a critical part of American history and deserves a greater place in the curriculum than the parenthesis to which it all often gets relegated. (A list of suggested readings and websites are included.)