Opposition to immigration exists in most nation-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 nation-state to another, where they are not citizens. The issue is complicated by the fact that there are various forms of immigration, and as such opposition to some forms of immigration does not always imply opposition to immigration as a whole. It is also important to distinguish between legal and illegal immigration in considering opposition to immigration. Illegal immigration is immigration in contravention of a nation’s immigration laws. The principal concerns expressed by those opposed to immigration are the perceived: economic costs (job competition and education and social services burdens); negative environmental impact from accelerated population growth; increased crime rates, protection against infectious diseases and, in some cases, the distortion of the national identity. There may also be a psychological component to prejudice against immigrants, with researchers showing that people are biased against immigrants partly because they find immigrants difficult to think about. In addition, when the immigration is illegal, opposition is focused on the economic and environmental costs and the violation of the receiving nation’s law. In cases such as the United States, where illegal immigration since the 1986 amnesty has resulted in an estimated 10-20 million illegal immigrants, the issue of failure of the rule of law itself is implicated. 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.