French writer Renaud Camus made the phrase popular in his 2011 book Le Grand Remplacement. The idea is much older. Madison Grant's 1916 book The Passing of the Great Race warned that immigrants would overrun white Americans, and it helped shape the Immigration Act of 1924. In the 1990s, white supremacists called the same fear "white genocide."
The theory went mainstream in the US in August 2017, when marchers in Charlottesville, Virginia, chanted "You will not replace us" and "Jews will not replace us." Shooters have used it to explain their attacks. They include the 2018 attack on the Tree of Life synagogue in Pittsburgh, the 2019 Walmart shooting in El Paso that targeted Latinos and the 2022 shooting at a Buffalo supermarket that killed 10 Black people. The man who killed 51 people at two mosques in Christchurch, New Zealand, in 2019 titled his manifesto "The Great Replacement."
The US is becoming more racially diverse because of births, immigration and changing family patterns. The conspiracy theory turns that change into a secret plot. A 2022 AP-NORC poll found that about 1 in 3 US adults believed there was an effort to replace native-born Americans with immigrants for political gain.