Immigration to the United States
Immigration to the United States has been a major source of population growth
Population growth
Population growth is the change in a population over time, and can be quantified as the change in the number of individuals of any species in a population using "per unit time" for measurement....

 and cultural change throughout much of the history of the United States
History of the United States
The history of the United States traditionally starts with the Declaration of Independence in the year 1776, although its territory was inhabited by Native Americans since prehistoric times and then by European colonists who followed the voyages of Christopher Columbus starting in 1492. The...

. 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
Social mobility
Social mobility refers to the movement of people in a population from one social class or economic level to another. It typically refers to vertical mobility -- movement of individuals or groups up from one socio-economic level to another, often by changing jobs or marrying; but can also refer to...

, crime, and voting behavior. As of 2006, the United States accepts more legal immigrants as permanent residents than all other countries in the world combined.