Most Americans believe that our military has been strengthened in the aftermath of the September 11 terrorist attacks; unfortunately, that is not the case. The core strength of American military forces has continued to erode. Of Men and Materiel: The Crisis in Military Resources, explores a problem that has been building quietly for years: The military has been expending without expanding or even replacing what has been spent. Today, our forces are stretched painfully thin by the grinding pace of operations in Iraq, Afghanistan, and elsewhere around the world. We have spent billions of dollars on the operational costs of these wars, but very little has been available to replenish the military's equipment or increase the size of the Army and the Marine Corps. The result has been a "hollow buildup." The closer one looks at this problem, the greater the strains and potential problems appear: Contributing authors Frederick W. Kagan, Loren Thompson, Robert Work, and Francis G. Hoffman examine the state of each branch of the military, underscoring a range of shortfalls in force strength, structure, and equipment. A simple truth emerges from each of these essays: a military that has less will do less. This is a dangerous situation for a nation with expansive foreign policy goals and global security commitments. The American military may well be the finest fighting force in history, but it cannot escape the fact that numbers matter. This is not the first time the United States has been confronted by sizeable gaps between its strategic ends and its military means, but the stakes in this battle have never been higher.