In arguing that racism was a major driver of Brexit and the transformation of British politics in the 2010s, this book proposes an interpretation of racism in general which may be new to some readers, as well as a distinctive concept of political racism. Racism is an obviously contested idea, in the double sense that there is no clear consensus on its meaning and application and that the differences about it matter in social and political conflict. It is also a relatively recent idea: Mark Mazower (1998: 103) dates racisme in French to the early 1930s, but its English equivalent only took over from the now quaint-sounding “racialism” around 1970. The use of the harder-sounding “racism” to describe racial hostility emerged in the Western world, therefore, long after “race” became a prominent feature of social relations and power in the world empires of European states, and only at the tail end of what Dirk Moses (2002) calls the “racial century” between 1850 and 1950 during which racial hierarchies achieved their most rigid forms. Indeed, it was only after racist political ideologies achieved extreme impacts in Europe itself during the Second World War, rather than in the colonized world where these had been obvious for centuries, that the modern critical idea of racism truly came into its own. Only then were the ideas of race which developed in the previous period – distinctions between human groups through biological and cultural differences and the discrimination and cruelty which accompanied them – deeply and widely contested within Western societies. Priyamvada Gopal (2019: 209ff.) shows that in Britain, it was between the world wars that anti-imperial insurgency in the colonized world combined with widespread dissidence in the metropolis to challenge the foundations of the racialized empire.