Every wave of terrorism has its intellectual point of departure. For Al-Qaeda's attacks in the West, it was Osama bin Laden's seminal Declaration of Jihad of 1996; in the case of Islamic State in Iraq and Syria-inspired terrorism, it was the announcement of the Islamic caliphate in 2014.

The current wave of white-supremacist terrorism, which recently manifested itself in lethal attacks against mosques in New Zealand and a synagogue near San Diego, can be traced back to a much less well-known event.