For years, Facebook and its CEO, Mark Zuckerberg, had defended Holocaust denial as a misguided but legitimate form of expression. In 2018, regarding Holocaust denial, he said, “I don’t believe that our platform should take that down because I think there are things that different people get wrong.”

That approach garnered widespread outcry from scholars and anti-Semitism watchdogs.

On Monday, Zuckerberg wrote in a Facebook post that he now believes banning Holocaust denial “is the right balance.”

“I’ve struggled with the tension between standing for free expression and the harm caused by minimizing or denying the horror of the Holocaust,” he wrote. “My own thinking has evolved as I’ve seen data showing an increase in anti-Semitic violence, as have our wider policies on hate speech.”

The change comes after months of activism by anti-discrimination groups pushing Facebook to change its policies on hate speech in general and Holocaust denial in particular. It also comes amid rising anti-Semitism in the United States and Europe, and weeks ahead of a presidential election that analysts and government agencies fear will spark violence from white supremacist groups.

This summer, the Anti-Defamation League, NAACP and other civil rights groups organized a boycott of Facebook in which 1,000 companies, including major corporations, paused advertising on the site for at least one month in protest of its lack of action against hate speech, including Holocaust denial. Other Jewish organizations worked in consultation with Facebook to persuade the site to ban Holocaust denial. Facebook’s statement credited the World Jewish Congress and American Jewish Committee with advising on the new policy.

It also cited a recent poll showing a lack of knowledge regarding the Holocaust among Americans younger than 40. The poll found that more than 10% of respondents believed Jews caused the Holocaust, while half of respondents said they had seen Holocaust denial online.

“By taking the critical step to remove Holocaust denial content, Facebook is showing that it recognizes Holocaust denial for what it truly is — a form of antisemitism and therefore hate speech,” World Jewish Congress President Ronald Lauder said in a statement. “Today’s announcement sends a strong message that Facebook will not allow its platform to be misused to promote hate.”

Facebook’s announcement of the new policy did not define what constitutes “content that denies or distorts the Holocaust.” And the social media giant said it “will take some time to train our reviewers and systems on enforcement,” and that deletion of Holocaust denial “cannot happen overnight.”

The new policy comes after Facebook tightened its restrictions on other forms of anti-Semitism and hate speech. Last week, Facebook announced that it was banning all groups and pages promoting QAnon, the anti-Semitic conspiracy theory. In August, Facebook banned posts about Jews controlling the world as well as other forms of hate speech.