Large numbers of people in the twelfth and thirteenth centuries migrated from one part of Europe to another in search of land, food, and work: the English into Scotland and Ireland; Germans, French, and Flemings into Poland, Bohemia, and Hungary; Christians into Muslim Spain. Everywhere in Europe, towns recruited people from the countryside as well. In frontier regions, townspeople were usually long-distance immigrants and, in eastern Europe, Ireland, and Scotland, ethnically different from the surrounding rural population. In eastern Europe, German was the language of the towns; in Irish towns, French, the tongue of Norman or English settlers, predominated. As a result of this colonization and movement to towns, peoples of different ethnic backgrounds lived side by side.

In the early periods of conquest and colonization, and in all regions with extensive migrations, a legal dualism existed: native peoples remained subject to their traditional laws; newcomers brought and were subject to the laws of the countries from which they came. On the Prussian and Polish frontier, for example, the law was that “men who come there … should be judged on account of any crime or contract engaged in there according to Polish custom if they are Poles and according to German custom if they are Germans.”10 Likewise, the conquered Muslim subjects of Christian kings in Spain had the right to be judged under Muslim law by Muslim judges.

The great exception to this broad pattern of legal pluralism was Ireland. From the start, the English practiced an extreme form of discrimination toward the native Irish. The English distinguished between the free and the unfree, and the entire Irish population, simply by the fact of Irish birth, was unfree. When English legal structures were established beginning in 1210, the Irish were denied access to the common-law courts. In civil (property) disputes, an English defendant did not need to respond to an Irish plaintiff; no Irish person could make a will. In criminal procedures, the murder of an Irishman was not considered a felony. Other than in Ireland, although native peoples commonly held humbler positions, both immigrant and native townspeople prospered during the expanding economy of the thirteenth century. But with the economic turmoil of the fourteenth century, ethnic tensions multiplied.

The later Middle Ages witnessed a movement away from legal pluralism or dualism and toward legal homogeneity and an emphasis on blood descent. The dominant ethnic group in an area tried to bar others from positions of church leadership and guild membership. Marriage laws were instituted that attempted to maintain ethnic purity by prohibiting intermarriage, and some church leaders actively promoted ethnic discrimination. As Germans moved eastward, for example, German bishops refused to appoint non-Germans to any church office, while Czech bishops closed monasteries to Germans.

The most extensive attempt to prevent intermarriage and protect ethnic purity is embodied in the Statute of Kilkenny (1366), a law the ruling English imposed on Ireland, which states that “there were to be no marriages between those of immigrant and native stock; that the English inhabitants of Ireland must employ the English language and bear English names; that they must ride in the English way [that is, with saddles] and have English apparel; that no Irishmen were to be granted ecclesiastical benefices or admitted to monasteries in the English parts of Ireland.”11

Late medieval chroniclers used words such as gens (race or clan) and natio (NAH-tee-oh; species, stock, or kind) to refer to different groups. They held that peoples differed according to language, traditions, customs, and laws. None of these were unchangeable, however, and commentators increasingly also described ethnic differences in terms of “blood,” which made ethnicity heritable. As national consciousness grew with the Hundred Years’ War, for example, people began to speak of “French blood” and “English blood.” Religious beliefs came to be conceptualized in terms of blood as well, with people regarded as having Jewish blood, Muslim blood, or Christian blood. The most dramatic expression of this was in Spain, where “purity of blood” — having no Muslim or Jewish ancestors — became an obsession. Blood also came to be used as a way to talk about social differences, especially for nobles. Just as the Irish and English were prohibited from marrying each other, those of “noble blood” were prohibited from marrying commoners in many parts of Europe. As Europeans increasingly came into contact with people from Africa and Asia, and particularly as they developed colonial empires, these notions of blood also became a way of conceptualizing racial categories.