The Great Replacement Theory is an ethno-nationalist theory warning that an indigenous European—e.g., white—population is being replaced by non-European immigrants. The Great Replacement concept was popularized by French writer Renaud Camus in his 2012 book, Le Grand Remplacement (“The Great Replacement”). Camus postulated that black and brown immigrants were reverse-colonizing native “white” Europeans.

Ethno-nationalist groups around the world such as the American Identity Movement and Generation Identity profess the Great Replacement Theory. These two specific groups claim to be non-violent, but others on the far right have used the Great Replacement Theory to justify violence. For example, Brenton Tarrant—who killed 51 people during attacks on two mosques in Christchurch, New Zealand, on March 15, 2019—titled his manifesto after the theory and warned of a white genocide. Patrick Crusius—who killed 21 people at a Walmart in El Paso, Texas, on August 3, 2019—also subscribed to the Great Replacement Theory. Violent white nationalists believe they are ensuring the survival of their own race through violence against other ethnicities.