This multidisciplinary review links three areas of legitimate inquiry for practitioners of medicine and public health. The first is occurrences of mass violence or genocide perpetrated against vulnerable populations, with a focus on the failure of national and international mechanisms to prevent or predict such violence. The second is evolving concepts of national sovereignty and an emerging framework in which the imperative to assist vulnerable populations supersedes a state's right to self determination. The last is how medical, public health, and other systems of surveillance and rapid assessment of mass violence can accelerate public awareness and facilitate structured, consistent political decision making to prevent mass violence and to provide international humanitarian assistance.

Let no one be discouraged by the belief there is nothing one man or one woman can do against the enormous array of the world's ills--against misery and ignorance, injustice and violence…. Each time he stands up for an ideal, or acts to improve the lot of others, or strikes out against injustice, he sends a tiny ripple of hope, and crossing each other from a million different centers of energy and daring those ripples build a current which can sweep down the mightiest walls of oppression and resistance. Robert F Kennedy

The principles of medicine and public health may help decision makers determine the timing and level of intervention to protect vulnerable populations from mass violence. Mass violence occurs overtly through warfare and civil strife, or covertly through the creation of morbid conditions, and here refers not only to homicide and genocide through direct injury but also to the promotion of other threats to the survival of populations, such as famine, drought, communicable disease, migration, and imprisonment. Mass violence and genocide are not homogeneous: their manifestations are quite diverse.1 Vulnerable populations include peoples identifiable by common …