A month after the international community solemnly marked the tenth anniversary of the Rwandan genocide in April 2004 with promises of "never again", it faces a man-made humanitarian catastrophe in western Sudan (Darfur) that can easily become nearly as deadly. It is too late to prevent substantial ethnic cleansing, but if the UN Security Council acts decisively -- including by preparing to authorise the use of force as a last resort -- there is just enough time to save hundreds of thousands of lives directly threatened by Sudanese troops and militias and by looming famine and set in train a serious negotiating process to resolve the underlying political problems and reverse the ethnic cleansing.