Growing up taking survival for granted makes people more open to new ideas and more tolerant of outgroups. Insecurity has the opposite effect, stimulating an Authoritarian Reflex in which people close ranks behind strong leaders, with strong in-group solidarity, rejection of outsiders, and rigid conformity to group norms. The 35 years of exceptional security experienced by developed democracies after WWII brought pervasive cultural changes, including the rise of Green parties and the spread of democracy. During the past 35 years, economic growth continued, but virtually all of the gains went to those at the top; the less-educated experienced declining existential security, fueling support for Populist Authoritarian phenomena such as Brexit, France’s National Front and Trump’s takeover of the Republican party. This raises two questions: (1) “What motivates people to support Populist Authoritarian movements?” And (2) “Why is the populist authoritarian vote so much higher now than it was several decades ago in high-income countries?” The two questions have different answers. Support for populist authoritarian parties is motivated by a backlash against cultural change. From the start, younger Postmaterialist birth cohorts supported environmentalist parties, while older, less secure cohorts supported authoritarian xenophobic parties, in an enduring intergenerational value clash. But for the past three decades, strong period effects have been working to increase support for xenophobic parties: economic gains have gone almost entirely to those at the top, while a large share of the population experienced declining real income and job security, along with a large influx of immigrants and refugees. Cultural backlash explains why given individuals support Populist Authoritarian movements. Declining existential security explains why support for these movements is greater now than it was thirty years ago.