A few of the most popular reasons for immigration to a country are religious tolerance and economic opportunity, though reasons vary between individuals and historical periods. Economists believe illegal immigration benefits the American economy by a small amount and chiefly harms unskilled workers, explains ProCon.org.
As of August 2014, experts estimate there are around 12 million undocumented immigrants living in the United States, according to the Australian Broadcasting Corporation. For most of its history, discourse around illegal immigration has been central to U.S. politics. The main concerns of most Americans involve preventing further illegal entry and handling those who have already entered.
The Harvard University Library Open Collections Program has documented the history of U.S. immigration. Many of the first immigrants to the United States voluntarily traveled from Europe for opportunity until 1619 when African slaves were forced to travel to America for the slave trade. In the late 1800s, anti-immigrant sentiments rose with the growing population, fear of contagious diseases and the belief that immigrants were inferior to citizens. Since this time, laws have put into place methods for limiting and restricting immigration, such as literacy tests, quota systems and the U.S. Border Patrol.