Buffalo, New York, 2022. Ten black people murdered. The killer, 18-year-old Payton Gendron, says he was driven by 'Great Replacement' - the conspiracy theory that a Jewish-led elite is replacing white people with black and brown people. This, and a spate of similar hate crimes, begs the question: what are the origins of such behaviour?Gavin Evans traces the historical roots of white supremacy. He begins in the 19th century with Charles Darwin and his cousin Francis Galton's race-based theories before looking at the spread of eugenics ideas throughout the UK, Europe and the United States, their Holocaust-prompted decline after the Second World War, and their revival in a different guise through the promotion of race science from the late 20th century. Evans also examines the hatching of 'Great Replacement' conspiratorial ideas in the 21st century - and their expression via alt-right forums to the minds of troubled young men with access to assault rifles. White Supremacy breaks new ground in showing the links between mainstream 'Replacement Theory' and the terrorist version cited by far-right killers. It also traces the thread between these ideas and the race science promoted both by the far right and establishment figures. It looks at what these ideas have in common with those promoted by, for example, the founder of eugenics.