As with Srebrenica in 1995, the potential for further mass killing in Darfur today is plain for all to see. All the warnings have been issued, including one from the United Nations that the coming weeks may see "a man-made catastrophe of an unprecedented scale." What remains unclear is only whether the world has the will to impose an outcome on Sudan different from that which unfolded so tragically in Bosnia. Make no mistake: At some point we will step in to help victims in Darfur and police an eventual settlement. The question is whether the United States and other nations will act now to prevent a tragedy, or merely express sorrow and act later to deal with its aftermath.