I would say that one of the most profound impacts of the Vietnam War on future foreign policy was to show the fallibility of a great power. Prior to the Vietnam War, there was a belief that guided the foreign policy of the United States that it could enter any realm and win any conflict from a military frame of reference. The entire idea of containment is one in which military presence automatically guarantees victory. The results of Vietnam was a reality check in which foreign policy had to be guided with the understanding that the United States might not win a particular contest. Unilateral and sweeping action might not be the formulas for military success. Since Vietnam, leaders of the United States have had to weigh the costs with "Could this be another Vietnam?" This question has become one of the lasting legacies of the war. "Vietnam" has come to mean a host of realities that were not in sight prior to it. Future foreign policies have been guided with this idea in terms of seeking to avoid a situation in which the metrics for victory are not clear, involvement of the United States lacks an exit strategy, and a situation in which public support becomes precarious. In the final analysis, this is where the Vietnam War cast its largest shadow on the foreign policies and decisions that came after it.