2007 marks 40 years since the launch of the movement to free Soviet Jewry, one of the defining developments in the Jewish world in the second half of the 20th century. In its honor, the US Senate will vote this week on a resolution commemorating the movement's founding following the Six Day War. "Forty years ago, in the depths of the Cold War, Americans from all walks of life came together to stand in solidarity with Soviet Jewry during its darkest hour," Sen. Joe Lieberman (Ind.-Connecticut), who co-authored the bill with Republican Sen. Arlen Specter of Pennsylvania, said this week. "Organizations like the National Council of Soviet Jewry gave voice to the voiceless millions of people trapped behind the Iron Curtain." The movement's success, the liberation of Soviet Jews from totalitarian communism, was the final stage of a dramatic reorientation of world Jewry. The exit of an estimated million and a half Jews, two-thirds to Israel and the rest mainly to North America, marks the most recent major exodus of Jews from Europe. In its wake, a Europe that began the 20th century as home to 85 percent-90% of the world's Jews finds itself at the start of this century with only some 15% of a much-reduced world Jewish population. Jews represent a perhaps unique victim of the ideological upheavals of Europe in the 20th century, becoming the only European people that has in effectively relocated en masse out of that continent. This century-long process, from the flight from Czarist oppression in the late 1800s to the "opening of the gates" for Soviet Jewry in the early 1990s, has both solved and created enormous challenges for modern Jewish security and cultural continuity. Three important lessons can be drawn from this unique experience. Looking back on the beginning of the Soviet Jewry movement in the US, one is struck by its improbability. At the time, the Soviet Union - a nuclear power run by a highly organized and ruthless regime that led the world in technological progress in numerous areas - constituted an existential threat to a politically polarized America mired in Vietnam. Hindsight cannot capture what must have seemed an immensely lofty goal. How likely was it that such a regime could be successfully opposed by foreign representatives of an oppressed minority that was barely a generation removed from the Holocaust? This is the political message of that movement. Challenges today facing the Jewish people may seem equally daunting: reaching a modus vivendi with the Palestinians; dealing with Mahmoud Ahmadinejad's fundamentalist Iran; developing a shared cultural language between the disparate communities of the Jewish world. One of the deep lessons of the Soviet Jewry movement is simply this: We need not be overwhelmed. The second important lesson concerns the power of Jewish peoplehood, particularly when post-Zionist voices in Israel claim an "Israeli peoplehood" separate from the Jewish one and some American social activists see in tikkun olam an ideal divorced from Jews' responsibility toward one another. The impossible task of resisting Soviet power was taken up with zeal by a wealthy and comfortable community of Jews on the other side of the world. Indeed, it became the galvanizing agenda that formed a generation of Diaspora Jewish leaders committed to carrying out the final liberation of the Jews from the last bastion of European repression. Today, American Jewry is unimaginable without the generation of activists that now fills central leadership roles. Third, the Soviet Jewry movement marked the end of a process that saw the complete restructuring of the Jewish world's demographics. For 2000 years, Jews were spread out in communities across many linguistic, ethnic and racial divides. But during the 20th century, world Jewry became overwhelmingly concentrated in just two - wholly different - Jewish cultures, one in the United States and the other in Israel. This created the deepest challenge of peoplehood in the 21st century. While the success of the Soviet Jewry movement teaches us the potential embedded in the concern of Jews for their brethren, the dichotomies between American and Israeli Jewry have created a nearly bipolar Jewish world whose centers of gravity are steadily drifting apart. The new Jewish world demands a generation of leaders that can find a shared transnational Jewish culture, a common ground not just of activism, but of culture and language, that will allow a united Jewish world to meet the challenges of the 21st century with the same success that it met those of the 20th.