The Expansion of the United States into Spanish areas following the Spanish-American War was a test of the vigor of American society in winning over groups that were essentially alien to it. With the annexation of territories such as Puerto Rico, the American way of life was, for the first time, operating on a culturally alien soil and was thus given the opportunity to show its capacity of being exported and adopted by a people who, as a group, were part of another cultural tradition. Puerto Rico has been for the last fifty years a small stage on which a culture drama was being played. American principles were introduced there together with American attitudes. Some patterns were imposed by American military and civilian authorities—often prompted by Puerto Ricans; others were imitated by the Puerto Ricans themselves. What was the climate of opinion that permitted this transfer, what were the methods employed to achieve it, and to what extent was it successful? These are the questions that come to the mind of the historian who studies Puerto Rico today.