The purpose of this book is to explore and examine the challenge to America's defense planners of needing to make purposeful and prudent choices in military preparation for the future. The problem for defense planning that is beyond resolution is the scientifically certain fact that we have no data from the future about the future. Moreover, this will always be a fact. No matter the scholarly discipline and tradition to which a defense planner owes or feels most allegiance, he or she needs to recognize and attempt to understand fully a personal and institutional condition of awesome ignorance of detail about the future. Further study, more cunning analytical methodology, even more powerful computers-none of these can reveal with any certainty what the future will bring. Fortunately, this does not mean that we are ignorant about the future; but it does mean that defense planning is guesswork and can only be such. Understandably, both senior policymakers and soldiers tend to be reluctant, even to the point of appearing to be evasive, when legislators question the plausibility of the answers given in congressional hearings. After all, it can be troubling to the conscience of honest and competent people to be obliged to affirm the integrity of choices made in defense preparation for national security in years to come, when there is and can be no certain way to know that one is sufficiently correct.