War played a major role in shaping the American economy in the twentieth century. In part this was because there was so much of it. If we include only the major hot wars, and use the official dates, then the United States was at war for roughly a quarter of the twentieth century. If we include the long Cold War, the figure rises to 55 percent. If we were to include the many smaller conflicts, the proportion of years in the twentieth century when American forces were fighting somewhere in the world would be still higher. To be sure, wars have produced many benefits. Few Americans would have been willing to contemplate the success of the Fascist nations, the most likely outcome had the United States remained neutral in World War II. The long war against Communism encompassing the Korean War, the Vietnam War, and the Cold War remains far more controversial. But here too, one can count benefits from the decisions to go to war. But wars have also been extremely costly, perhaps more so than is generally realized because politicians often do the best they can to hide the costs of war.