The mass shooting at the Tree of Life synagogue in Pittsburgh comes amid a wave of rightwing violence across the US fuelled by conspiracy theories. It is also part of a long history of white supremacist terror aimed at American Jewish communities.

The murder of 11 people and wounding of six, allegedly by Robert Bowers, 46, came a day after the arrest of Cesar Sayoc, 56, for a mail bombing campaign that targeted liberals including George Soros. A prominent Jewish billionaire, Soros has in recent weeks been the target of heightened conspiracy-minded rhetoric from prominent Republicans including Donald Trump.

A social media post that appeared to be Bowers’ last before the attack was an attack on HIAS, a Jewish-run refugee charity, which he accused of working to “bring invaders in that kill our people”.

This belief is in keeping with white supremacist “white genocide” narratives, which hold in part that Jews are orchestrating the “demographic replacement” of white people by means of immigration.

It also resembles recent conspiracy-minded comments by mainstream Republicans about the so-called “caravan” of Honduran refugees which is currently hundreds of miles from the US southern border.

On 17 October, the Florida congressman Matt Gaetz sent out a tweet that read: “Footage in Honduras giving cash 2 women & children 2 join the caravan & storm the US border @ election time. Soros? US-backed NGOs? Time to investigate the source!” While attempting to explain the tweet, he made a similar charge about Soros and the Balkans.

It was also reported last week that the Iowa congressman Steve King had aired white-nationalist style views about demographic replacement in an interview with a far-right Austrian website.

On Saturday, Heidi Beirich, director of the Intelligence Project at the Southern Poverty Law Center (SPLC), which monitors hate groups, said Gaetz’s tweet was a “soft version” of the white genocide theory.

Beirich added that “sections of the far right, including the president, have fallen into a fever swamp” concerning Soros. Earlier this month, Trump tweeted the assertion that the financier paid activists protesting against the nomination of Brett Kavanaugh to the supreme court. During the 2016 election, his final campaign ad connected Soros and the then Federal Reserve chair, Janet Yellen, with a supposed “globalist” establishment conspiracy.

Beirich said those who deploy such rhetoric “absolutely bear a moral responsibility” for acts of antisemitic violence such as that which took place in Pittsburgh.

The Anti-Defamation League (ADL) chief executive, Jonathan A Greenblatt, released a statement on Saturday in which he said the shooting was “likely the deadliest attack on the Jewish community in the history of the United States”.

He added that it came at a “time when ADL has reported a historic increase in both anti-Semitic incidents and anti-Semitic online harassment”.

The statement pointed to ADL research showing large increases in antisemitic incidents and antisemitic online harassment.

Over the last two decades, white supremacists have repeatedly targeted synagogues and other Jewish institutions for vandalism and violent attacks.

On 13 April 2014, Frazier Glenn Miller Jr, a neo-Nazi, shot dead three people at a Jewish community center and a retirement home in Overland Park, Kansas.

In 2002, Jake Laskey, his brother Gabriel Laskey and two other men threw swastika-engraved rocks at Temple Beth Israel in Eugene, Oregon, during Friday prayers. In 1994, the same synagogue was the target of a drive-by shooting by a member of the neo-Nazi American Front group, which desecrated several synagogues in the 1990s.

On 10 August 1999, Buford O Furrow Jr fired 70 shots into the Jewish Community Center in Granada Hills near Los Angeles, wounding five people.

Beirich pointed out that synagogues were firebombed during the civil rights era and have retained “an enormous symbolic importance” for white supremacists. The main intention in attacking them, she said, was to terrorize Jews.

“The thing about hitting a house of worship is that you make everyone in that community frightened,” she said. “If you’re a white supremacist, you can’t hit a better target.”

The journalist David Neiwert, author of books on the far right including The Eliminationists, which details how hate speech has radicalized the US right, said antisemitic conspiracism, “which is being promoted at the highest levels of government and media”, leads to violence from some who believe it.

“It convinces them that their fellow Americans are part of a nefarious plot to destroy American society, and gives them permission to kill,” Neiwert said. “It is the driver in the spate of domestic terrorism the country is currently experiencing.”