Sociologists have studied immigration closely in the twenty-first century. In the United States, compared to the majority of European immigrants during the early twentieth century, the twenty-first century witnessed the arrival of immigrants predominately from Asia, the Middle East, and Latin America. From 2000 to 2001, sociologists have paid particular attention to the costs and benefits of the new diversified immigration population on American institutions, culture, economic functions, and national security. After the attacks on the World Trade Center and the Pentagon on September 11, 2001, sociologists closely analyzed the symbolism of increased anti-immigration rhetoric, directed at Middle Eastern immigrants, stemming from Americans. Structural functionalist theorists have also studied the effects of mass migration—resulting from wars, economic insecurity, and terrorism—on the social institutions of host nations, on international law, and on assimilation rates. Additionally, sociologists using social-conflict theory have analyzed, in particular, labor-market conflicts allegedly resulting from increased marketplace competition due to the rise in competition between immigrants and native workers for jobs and social mobility. Because rates of global immigration continue to increase, the field of sociology has a particular interest in monitoring twenty-first century immigration as it relates to the foundational theories of symbolic interactionism, social conflict, and structural functionalism.