Opposition to immigration exists in most states with immigration, and has become a significant political issue in many countries. Immigration in the modern sense refers to movement of people from one state or territory to another state or territory where they are not citizens. Illegal immigration is immigration in contravention of a state's immigration laws.
In the United States, the principal concerns expressed by those opposed to immigration are the perceived effects economic costs (job competition and burdens on education and social services); negative environmental impact from accelerated population growth; increased crime rates, and in the long run, changes in traditional identities and values. In Spain, surveys show the issues that arouse most controversy are, "in descending order, jobs, crime and housing."
In countries where the majority of the population is of immigrant descent, such as the United States, opposition to immigration sometimes takes the form of nativism targeted primarily at 'first-generation' immigrants.
Some critics of immigration argue that the presence of immigrants may distort the national identity of the native population. That means that the native population opposes immigration because they fear they may lose their sense of belonging to their own nation, as represented by distinctive traditions, culture, language and politics.
National identity can be an important factor for social peace in cases where there are intra-national divides. For example, a 2015 study showed that the educational content of Suharto's Indonesia emphasizing the national unity of Indonesia was an important cause of improved inter-ethnic and inter-religious relationships.
If native societies fail to integrate immigrants they quite often blame the immigrants themselves for it: National unity arguments are, for example, if immigrants isolate themselves in their own communities and refuse to learn the local language, this may eventually undermine the national unity, as well as the cultural and religious unity of the native country. As a consequence the immigrants may form ghettos where they live according to their own culture, rather than assimilating to the native culture. They may live in self-organized communities, or parallel societies, with the intent of a reduced or minimal spatial, social and cultural contact with the majority society into which they have immigrated.