Hostility toward or discrimination against Jews as a religious group or race. Although the term anti-Semitism has wide currency, it is regarded by some as a misnomer, implying discrimination against all Semites, including Arabs and other peoples who are not the targets of anti-Semitism as it is usually understood. In antiquity, hostility to the Jews emerged because of religious differences, a situation worsened as a result of the competition with Christianity. By the 4th century, Christians tended to see Jews as an alien people whose repudiation of Christ had condemned them to perpetual migration. Jews were denied citizenship and its rights in much of Europe in the Middle Ages (though some societies were more tolerant) or were forced to wear distinctive clothing, and there were forced expulsions of Jews from several regions in that period. Developed during the Middle Ages were many of the stereotypes of Jews (e.g., the blood libel, alleged greed, conspiracy against humankind) that have persisted into the modern era. The Enlightenment and the French Revolution brought a new religious freedom to Europe in the 18th century but did not reduce anti-Semitism, because Jews continued to be regarded as outsiders. In the 19th century violent discrimination intensified (seepogrom), and so-called scientific racism emerged, which based hostility to the Jews on their supposed biological characteristics and replaced religion as the primary basis for anti-Semitism. In the 20th century the economic and political dislocations caused by World War I intensified anti-Semitism, and racist anti-Semitism flourished in Nazi Germany. Nazi persecution of the Jews led to the Holocaust, in which an estimated six million Jews were exterminated. Despite the defeat of the Nazis in World War II, anti-Semitism remained a problem in many parts of the world into the 21st century.