Few phenomena affecting Western Europe as a whole have been more far-reaching in their immediate effects or more potentially destabilizing to society and politics over the longer term than the accumulative experience of post-WWII immigration. Accelerating with the explosion in the number of asylum seekers, refugees, and illegal migrants gaining entrance to Western Europe during the 1980s and beyond, the phenomenon of post-WWII immigration has profoundly challenged states, governments, and societies in ways that could hardly have been anticipated when the first wave of foreign workers began to arrive in Western Europe a half century ago (Joppke 1999a). As a direct result of the sociocultural conflict between minority and majority populations and, in some countries, between the new ethnic minorities and the state, ethnicity has now become more salient as a political and social cleavage in Western Europe than at any time since World War II (Fetzer and Soper 2004; Modood and Werbner 1997; Wicker 1997). In Belgium, France, Spain, Switzerland, and the United Kingdom, new ethnic cleavages have been superimposed over the old (Messina 1992).