Leaders from almost 50 countries gathered here Thursday to mark 75 years since the liberation of Auschwitz and, drawing on the memory of its horrors, to mount a united stand against the resurgence of anti-Semitism around the world.

Vice President Pence and Speaker of the House Nancy Pelosi were among the dignitaries and delegations filling Yad Vashem, the city’s somber memorial to the Holocaust’s 6 million Jewish victims, for the World Holocaust Forum, one of the largest international events ever hosted by Israel.

Leaders of World War II’s four allied powers addressed the body, including Pence, Britain’s Prince Charles, French President Emmanuel Macron and Russian President Vladimir Putin, along with German President Frank-Walter Steinmeier, Israeli President Reuven Rivlin and Prime Minister Benjamin Netanyahu.

With about 100 of the fast-dwindling number of Holocaust survivors present, participants warned that the hatred that fostered the industrial murder that took many of their families is festering again in incidents both trivial and terrorizing, from swastikas painted on gravestones to mass shootings at synagogues.

Now is the time, organizers said, to turn honoring the victims of the Holocaust into a real-time call to action.

“Ladies and gentlemen, I commit that those words, ‘Never Again,’ will not be an empty slogan, but will be an ongoing decree, an imperative that must be followed,” said Netanyahu. He called the unprecedented gathering “a sign of hope.”

Rivlin warned that “if we do not remember, then history can be repeated.”

“Anti-Semitism is a chronic disease,” Rivlin said. “It comes from left and right, taking on and discarding forms during history.”

Moshe Kantor, the Russian philanthropist and president of the World Holocaust Forum Foundation who organized the gathering, compared the moment to attempts by world leaders to address rising anti-Jewish violence in Europe eight decades ago at a conference in Evian, France.

“This meeting ended up with no agreement and no result,” Kantor said in an interview, a failure that paved the way for the atrocities that followed. “This is why the level of anti-Semitism in the world should serve as a moral barometer.”

President Trump, who has been criticized for not condemning anti-Semitic rhetoric by some of his supporters, including at a 2017 white supremacist rally in Charlottesville, did not attend the forum. But along with other heads of state, the president did provide a comment to be collected in a commemorative album about the event.

“We have a fundamental and collective duty to ensure that each new generation knows the truth,” Trump wrote. “The lessons of the Holocaust must forever be engrained in the consciousness so that we can fulfill our solemn and sacred promise that such evil and hatred will never again come to power.”

Pence, in his remarks, joined the call to link historic atrocities — such as those exposed when Soviet soldiers entered the gates of Auschwitz — with more recent offenses.

“We must confront and expose the rising tide of vile anti-Semitism fueling hate and violence across the broader world,” Pence said.

He and Netanyahu both singled out Iran as a particular threat. ,Pence said Tehran is the “one government in the world that denies the Holocaust as a matter of state policy and threatens to wipe Israel off the map.”

Prince Charles, whose paternal grandmother Princess Alice is honored by Israel for hiding a Jewish family in Athens during the Holocaust, cited his personal connection to many survivors, and to today’s victims of hatred.

“The Holocaust must never be allowed to become simply a fact of history,” he said. “We must be vigilant in discerning these ever-changing threats.”

The gathering of the World Holocaust Forum all but took over the Holy City, closing streets and schools and drawing more than 11,000 security officers from around the country and some 500 journalists from around the world (including 107 who came with Putin). Hotels scrambled to accommodate presidents and princes as motorcades filled roads otherwise as quiet as a Saturday sabbath.

With the city overbooked with world leaders, the U.S. delegation, not headed by a head of state, was staying not in one of the luxury hotels near the Old City, but at the local Crown Plaza, a hotel better known for bus tours of young visitors than high-level diplomacy.

Many of the participants were traveling straight from another global gathering, the World Economic Forum at Davos, Switzerland. Among those who had planned to make the trip was Jared Kushner, Trump’s son-in-law and keeper of the long-delayed White House “Deal of the Century” peace proposal between Israel and the Palestinians.

Kushner, however, canceled his stop in Jerusalem on Wednesday, citing potential weather-related flight delays and quashing speculation, for now, that the debut of “the deal” was imminent.

Plenty of other politicians did find their way into the solemn gathering, however. Macron caused a stir when he was shown shouting at Israeli security personnel as he was entering the Church of St. Anne, a medieval edifice owned by the French government. The vocal dispute apparently had to do with whether French or Israeli security would escort Macron into the nave, a reflection of the byzantine turf conflicts that riddle Jerusalem’s holy sites. (Control of the nearby Church of the Sepulcher is divided among six separate Christian sects.)

Andrzej Duda, president of Poland, where Auschwitz and other Nazi concentration camps were located, boycotted the gathering entirely in protest of not being offered a speaking role at the Yad Vashem ceremony. The perceived snub came amid a growing blame-game between Poland and Russia over who started World War II. Duda has accused Putin of spreading a “historical lie” about Poland’s willingness to help the Nazis while downplaying Russia’s own nonaggression pact with Germany. Duda will attend commemorative events at Auschwitz on Monday.

Locally, though, Israelis were fixated on Putin, particularly whether he would use his visit to announce the release of a 27-year-old American Israeli backpacker imprisoned in Russia on minor drug charges. The case is widely seen as part of a wider geopolitical tussle between Russia and the United States, including efforts by Washington to have an alleged Russian hacker extradited from Israel.

The plight of the New Jersey-born Na’ama Issachar, who was found with a small amount of hashish when transiting the Moscow airport on a flight from India, has become a cause celebre here. “Free Na’ama” signs hang over highways, and her mother has become a frequent, pleading presence on television.

Putin appeared with the mother Thursday after meeting Netanyahu at the prime minister’s residence, telling her that “everything will be fine” and promising to consider her request to let her daughter come home.

Pence was also scheduled to meet with Netanyahu, and the prime ministered personally welcomed Pelosi and the U.S. congressional delegation. Both also met briefly with Benny Gantz, the former Israeli army chief who is Netanyahu’s main rival in a year-long political standoff. Israel is holding its third election in a year in March, with the prime minister under indictment on corruption charges.

Another fraught encounter is possible for Pence in the person of Ukrainian President Volodymyr Zelensky, the leader at the center of impeachment proceedings in Washington. Pence skipped Zelenksy’s inauguration in May at a time when Trump was seeking to pressure the Ukrainian to investigate a Democratic rival.

It was unclear if the two would bump into each other on the Yad Vashem stage, however. Zelensky reportedly surrendered his seat during the main ceremony at Yad Vashem to Holocaust survivors.

Pence was also planning a visit with his wife to the Western “Wailing” Wall in Jerusalem’s Old City. Putin was slated to visit the West Bank city of Bethlehem for a meeting with Palestinian Authority President Mahmoud Abbas.

Putin attended the dedication of a new Jerusalem memorial to the Siege of Leningrad in the 1940s. About 800,000 people died during the more than two years the city, now known as St. Petersburg, was under siege, including many Jews.

More than a million Russian-speaking Jews emigrated to Israel after the fall of the Soviet Union in the early 1990s, and they have carved out a central role in Israeli politics and culture. The memorial, a soaring bronze tower, was funded by Jewish organizations and the city councils of St. Petersburg and Jerusalem.

Russian immigrants are a growing presence in Israeli politics and culture, and the memorial, a soaring bronze tower, was funded by Jewish organizations and the city councils of St. Petersburg and Jerusalem.