Is far-right terrorism on the rise in the West? It is hard to be sure. Only the most extreme forms of violence, such as murders, are reliably reported to the police. Perpetrators’ motives are not always clear. And defining terrorism is hard. Not every racist murder is intended to spread fear for political purposes.

Whether white nationalist or Islamist terrorism has been more deadly in Western countries depends on how each incident is classified. Estimates differ widely. The Anti-Defamation League, a pressure group, finds that “right-wing extremism” was responsible for 73% of “domestic extremist-related killings” in the United States from 2009-18, and that “Islamist extremism” accounted for 23%. In contrast, the Study of Terrorism and Responses to Terrorism (START) database, compiled by the University of Maryland, says that jihadists carried out roughly twice as many terrorist murders in the United States during that period as right-wingers did.

The Christchurch assailant frequented white supremacist corners of the internet. Many terrorists, whether jihadists or white nationalists, gain inspiration in this way, and make contact with others who share their views. START data on terrorist attacks in North America, western Europe and Oceania seem to support the theory that social media can help turn extremists into violent extremists: a spate of right-wing terrorist attacks broke out after a lull in the early-to-mid 2000s, just as such media began to gain popularity.

The media generally find jihadist attacks more newsworthy than right-wing ones. A recent study by Erin Kearns of the University of Alabama analysed media coverage of terrorist attacks in America from 2006-15. Ms Kearns finds that terrorist attacks perpetrated by Muslims received 360% more press coverage than comparably sized attacks carried out by others.