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."
Opposition to immigration ranges from opposition to any immigration to ones nation to calls for varying kinds of immigration reforms that further restrict immigration and may go hand in hand with measures to fight causes of flight.
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.
Immigrants may isolate themselves in their own communities, forming self-organized communities, ghettos or parallel societies where they live according to their own culture, rather than assimilating to the native culture with a reduced or minimal spatial, social and cultural contact with the majority society into which they have immigrated. Such ethnic enclaves can be the result of humans naturally liking to be around people like themselves. They might not learn the local language and might eventually undermine the national unity, as well as the cultural and religious unity of the native country. Research by Jennifer Neal of Michigan State University suggests that ethnic enclaves promote social cohesion at the cost of decreasing tolerance between groups and that their size, autonomy and proximity are factors. Some also suggest to devolve more power to local communities.