Immigration to the United States is the international movement of individuals who are not natives or do not possess citizenship in order to settle, reside, study or to take up employment in the United States. It has been a major source of population growth and cultural change throughout much of the history of the United States. The economic, social, and political aspects of immigration have caused controversy regarding ethnicity, economic benefits, jobs for non-immigrants, settlement patterns, impact on upward social mobility, crime, and voting behavior.