International migration is not simply a result of individuals' search for better opportunities, but is also linked to a complex series of economic and geopolitical processes. It is also an especially important interpretive key through which to understand the long history of globalization. For Castles and Miller, migration is a collective action that increasingly changes the social, political, economic, and cultural landscape of the world. According to Mauss, it is a fait social total. Over the last 20 years, an increasing number of countries have experienced a prolonged transition in the nature of the migration to which they are subject: countries that were historically lands of emigration are becoming lands of immigration, for example Italy, Greece, Spain, Portugal, and Ireland. Societies, and especially destination and departure countries, are inextricably interrelated through this phenomenon.