Racisms: From the Crusades to the Twentieth Century, By Francisco Bethencourt: Book review

Bulgarian benefit tourists, Romanian criminal gangs, the alleged abduction of a blonde, blue-eyed child by Roma: anti-immigrant hostility is more pronounced in Britain than any time in a generation. With it have come a raft of questions about race and national identity that were once confined to the fringes of public debate. Is Britain full? Is our way of life at breaking point? Is it racist to raise such points? And come to that, what exactly does racism mean in a modern, multicultural nation like Britain anyway?

Answers, especially to the last question, often prove elusive. That's because racism is often treated as a subject too charged, too sensitive to address head-on. It's easier to see it instead as an ugly but inescapable fact of life, a failing common to all nations when different groups decide they can't get along. But history also offers examples of societies where intolerance, unchecked, has triggered horrifying consequences.

In 1915, the Ottoman Empire began a brutal campaign of discrimination against its Armenian minority that escalated from arrests and property seizures into mass deportations, the burning of families and death marches into the Syrian desert. Over the following year about a million Armenians died in the first historical example of genocide by a state against a specific national minority. There are numerous other instances of national policy based on prejudice, from further cases of genocide in Nazi Germany and Pol Pot's Cambodia to the iniquities of the Jim Crow South and apartheid South Africa.

How does discrimination on this scale occur? What does it take for prejudice to become the rationale for segregation or enslavement or racial extermination?

This is the subject of Francisco Bethencourt's ambitious and wide-ranging Racisms, which tracks the evolution of a pernicious belief system from the Crusades to the present day. Focused primarily on Western history, Bethencourt's thesis is that racism can't simply be thought of as a naturally occurring, universal aspect of human behaviour. Instead racism is "relational", the result of specific economic or political circumstances that create the context for extreme intolerance.

For instance the climate of murderous bigotry that led to the Armenian genocide was triggered by the losses in battle of Ottoman forces during World War I and a desire to find a scapegoat for national failure. As Europeans ventured overseas during the 16th and 17th centuries, they justified their territorial ambitions in Africa and the Americas with lurid tales of cannibalism, idolatry and debauched sexual practices among the indigenous peoples they encountered there. In 1990s Rwanda, conflict over power and natural resources was expressed in racialised terms, with the Tutsi minority vilified by Hutus as cockroaches, the deserving subject of genocide.

Each of these cases is unique in their circumstances and their rationale for discrimination. And for Bethencourt there is no one single type of racism practiced by nations through history, no group that is universally discriminated against –hence the pluralised title of his book. However, where those racist regimes are linked is through a shared belief in the sanctity of blood. Bethencourt describes racism as "prejudice concerning ethnic descent coupled with discriminatory action".

This admirably succinct description goes to the core tenet of racist ideology, which is that physical or cultural characteristics are passed by blood from generation to generation. Fear of contamination of bloodline, and of the body politic itself, becomes the justification for the racist policies of a host of countries otherwise separated by time and geography, from the one drop rule of the American South to the violent expulsion from Spain of Christian descendants of Muslims in 1609 and the anti-Jewish pogroms in civil war Russia in 1917, led by the White army under the slogan, "Beat the Yids and save Russia".

The fact that beliefs around descent have prevailed across the centuries is largely down to the ambiguous nature of the term race itself. The word was coined in the Middle Ages in connection to the raising of plants and animals. It gained an ethnic dimension around the 16th century to describe an impurity in the blood of Jews and Muslims. Over time, race gained multiple meanings, as a synonym for nationality, gender and varieties of human beings in general.

In the 19th century it also acquired a hierarchical character, as natural historians such as Georges Cuvier and Robert Knox equated race with cultural development, drawing a lineage of human progress from the civilised Caucasian to the savage Ethiopian. Today, science has made a nonsense of the entire biological basis of race, having found greater genetic variation between people of the same skin colour than between say blacks and whites. Yet even with no grounding in fact the myth of racial difference, of types of behaviour inherent to different ethnicities or peoples, persists.

Bethencourt traces its origins to the publication in 1570 of the first significant printed atlas of the world by the Flemish cartographer Abraham Ortelius. The frontispiece of the atlas carried an illustration of Europe, Africa, Asia and America, personified as women, each with a clearly identifiable set of virtues or vices. Seated on an elevated throne was Europe, the embodiment of wisdom, justice and ethics. Asia, courteous, honourable, but also capable of great cruelty and depravity, stood below. Beside her was Africa, wearing only a loose cloth around her hips to indicate her lascivious, barbaric character. America lay naked at their feet clutching a severed head; a reference to the popular image of the continent's people as conscienceless cannibals. Ortelius' atlas was enormously influential, going through 41 editions and setting the template for ideas about race and national identity that continue to resonate today.

As the immigration debate in Britain becomes more heated, its rhetoric more inflammatory, it's all the more important to trace the historical context for our understanding of otherness. Racisms is a dense, closely argued work resistant to browsing. But its cataloguing of successive centuries of poisonous bigotry, of tangled, self-serving myth and murderous victimisation, creates a powerful cumulative effect. To chart some of my own emotions while reading it: anger; pain, disgust and sorrow. This is an unlovely history. But a necessary one that appears, sadly for the wrong reasons, at the right time.