Tonight, as Holocaust Memorial Day begins, we remember the six million Jews who were systematically murdered by Nazi Germany. As we do so, it is not just the passage of time that makes it difficult to imagine the enormity of this crime, the suffering of the victims and the implications for the human condition. Since the Holocaust, the Jewish people - already commanded to remember its long history - has become obsessed with commemorating an atrocity greater than the many it had already experienced. Holocaust museums have become ubiquitous, as Jews have rightly argued that this crime cannot be viewed merely through the narrow lens of anti-Semitism, but must be seen as a challenge to all peoples and to all future generations. The challenge is expressed in the resonating words: Never again. It is this challenge that animated the founding institutions and concepts of the post-war international order - the United Nations, the Genocide Convention, the Universal Declaration of Human Rights, the notion of war criminals and their prosecution. But these institutions and the nations behind them failed to prevent genocides in Cambodia and Rwanda, and massacres and ethnic cleansing in Bosnia, and are now failing in Darfur. The universalist cry "never again" rings hollow. The Committee of Conscience, a body established by the council that oversees the US Holocaust Memorial Museum in Washington, has categorized current humanitarian crises according to urgency. The committee has issued a "watch" on the situation in Chechnya and, since 2004, an "emergency" (meaning that "acts of genocide or related crimes against humanity are occurring or immediately threatened") regarding Darfur (see www.ushmm.org/conscience/alert). It is, of course, more than appropriate for Holocaust museums to see their role not just in terms of displaying the past, but affecting the present and the future. Last month, Yad Vashem took Sudanese refugees in Israel on a special tour of the museum. "People were supposed to learn from history," one of them responded. "But still it happens now. In 1994 in Rwanda and now in Darfur. I thought the world was supposed to learn." In this vein, just after the Iranian regime hosted Holocaust deniers in Teheran, Yad Vashem convened a briefing for the diplomatic corps titled "Holocaust Denial: Paving the Way to Genocide." Yad Vashem Chairman Avner Shalev explained, "Iranian President [Mahmoud] Ahmadinejad has made Holocaust denial part of a strategic agenda; not an academic or intellectual issue. Ahmadinejad wants to lead an Islamic jihad and to orchestrate another genocide aimed at destroying the State of Israel." At this event, Yosef (Tommy) Lapid, a Holocaust survivor and former justice minister who now chairs Yad Vashem's council, said, "If Europe missed the opportunity to understand what Hitler was promising, then Europe should believe what the Iranian president is saying now. He means business. The entire Judeo-Christian tradition is in a battle for survival against radical Islam." Seven years into the 21st century, the situation is this: Having failed in the universalist attempt to prevent genocides and war crimes in Asia, Africa and even in the heart of Europe, and failing now to stop a genocide in Darfur, we are now facing a turning back of the clock to the 1930s, in which new tyrants threaten both genocide and world war. And once again, at the epicenter of this threat, stands the Jewish people. It is not too late to stop Iran. The mullahs, beset by bitter and growing opposition at home and by internal power struggles, cannot withstand a full diplomatic and economic boycott imposed by Western nations. It still may be possible to avoid the need for military action. What is abundantly clear, however, is that jihadist Iran, like Nazi Germany, will not stop until it is stopped. As in the 1930s, a refusal now to employ sufficient nonmilitary means to confront megalomanical tyrants now will not avoid war, but precipitate it. The Jewish people must not flinch from sounding this alarm. To paraphrase the sage Hillel, if not the Jews, then who? And if not now, then when?