“Monuments Man” James Rorimer, with notepad, supervises U.S. soldiers as they carry paintings down the steps of the castle in Neuschwanstein, Germany, in May 1945. (AP)

Stuart E. Eizenstat was under secretary of state and special representative of the president and secretary of state on Holocaust-era issues in the Clinton administration and is expert adviser to the State Department on Holocaust-era issues in the Trump administration.

During World War II, the Nazis looted some 600,000 paintings from Jews, at least 100,000 of which are still missing. The looting was not only designed to enrich the Third Reich but also integral to the Holocaust’s goal of eliminating all vestiges of Jewish identity and culture. The Allies warned neutral nations in the 1943 London Declaration against trafficking in Nazi-looted art. Art experts, the storied “ Monuments Men ,” were embedded in the liberating U.S. Army. The looted wealth they preserved was returned to the countries where it had been stolen in the expectation that the original owners or their heirs would receive it. That hope was misplaced: Most items were sold or incorporated into public and private collections, lost to their rightful owners.

Decades later, in December 1998, we started to change that. Forty-four countries committed to the Washington Principles on Nazi-Confiscated Art that I negotiated for identifying, publishing and ultimately restoring the looted art through negotiation. To achieve a consensus, we had to permit nations to act within their own laws, and appealed to their moral conscience to adopt a “just and fair solution.” Many felt these nonbinding principles would be ineffectual. They were wrong, but the lack of legal requirement has created barriers we have yet to fully overcome.

The principles were an overdue but vital first step. Philippe de Montebello, then-head of New York’s Metropolitan Museum, correctly forecast that after the Washington Principles “the art world would never be the same.” During the past 20 years, galleries, dealers and museums began researching paintings that had passed through European hands between 1933 and 1945 to spot suspicious gaps in their provenance or chain of ownership. With the Internet, suspected Nazi-looted art is increasingly being posted on websites. Almost 30,000 works from their collections have been posted by 179 members of the American Alliance of Museums on a portal, a single point of contact for potential claimants to find their Nazi-looted art.

Austria, France, Germany, the Netherlands and Britain have created advisory commissions to resolve disputed claims. Austria has returned more than 30,000 artworks, books and cultural objects, and Germany has restituted more than 16,000 from its public museums and libraries. Christie’s and Sotheby’s maintain full-time staffs to implement the Washington Principles, and both auction houses decline to deal in art with suspicious Holocaust-era histories. Christie’s has successfully resolved more than 200 claims over the past 20 years. In 2009, the principles were strengthened by the Terezin Declaration, when 46 countries, led by the United States, agreed to extend the Washington Principles to include “public and private institutions” and broaden the meaning of confiscated art to include “forced sales and sales under duress” for Jewish families desperately needing money to escape Nazi Germany.

There have been painful disappointments. Russia and a handful of other European nations that supported the Washington Principles have largely ignored or barely implemented them. Provenance research is a low priority in Europe’s public museums and nonxistent in its private collections; looted art still trades in the European market with little hindrance. Deaccession laws prevent public museums from returning art under any circumstances.

Fortunately, the Washington Principles continue to exert a moral force. With bipartisan support, Congress in 2016 created a unique federal statute of limitations preempting other defenses related to the passage of time and providing six years to file a claim only after a claimant has discovered the identity and location of the artwork. In 2018, Congress passed another law instructing the State Department to report on the restitution record of all 46 countries that endorsed the Terezin Declaration. And in late November, more than 1,000 representatives and stakeholders from more than 10 countries gathered in Berlin for three days to measure our progress after 20 years and chart a road map for next steps. The Trump administration sent Special Envoy for Holocaust Issues Thomas Yazdgerdi and me to recommit to the international effort to return these personal and cultural treasures to the families to which they belong. We know this is the work of more than any single administration, indeed more than any single generation.

France has just given the prime minister’s office new authority to resolve claims and facilitate restitution. Cooperation has begun between major German and American museums. Germany has significantly increased funding for provenance research and set a goal to complete a comprehensive database of its federal museums by 2020. Germany will no longer permit its federal museums to block claims for restitution simply by refusing to participate in mediation. Germany and France announced initiatives to review art taken from their former colonies, and the European Parliament is considering legislation to endorse the Washington Principles and develop rules for cultural objects stolen in future conflicts.

No self-respecting government, art dealer, private collector, museum or auction house should trade in or possess art stolen by the Nazis. We must all recommit to faithfully implementing the Washington Principles before Holocaust survivors breathe their last breath. We owe it not only to those who lost so much in the Holocaust but also to our own sense of moral justice.