"The concept of Manifest Destiny, with its assertion of racial superiority sustained by military power, has defined U.S. identity for 150 years. Only the Vietnam War brought a serious challenge to that concept of almightiness. Bitter debate, moral anguish, images of My Lai and the prospect of military defeat for the first time in U.S. history all suggested that the long-standing marriage of virtue and violence might soon be on the rocks."