US laws declare that any alien entering into the country without legal documents or over staying beyond the expiration of visa date, consequently violating the immigration rules is considered as an illegal immigrant. It has been a persisting problem in US since 19th century but became more predominant in the last two decades. During the periods from 1881 to 1920, almost 23 ½ million immigrants entered into US from all over the world but later, congress passed many restrictions on the immigration quota lowering the legal immigration entries. This restraint lead to more illegal immigrations from different nationalities but 75% of undocumented immigrants arrived from south Mexico border mostly from Colombia, El Salvador, Mexico and other South American countries.
It is very difficult to conclude on the exact number of illegal immigrations but as the history would show, majority of these illegal aliens were not highly qualified and worked as cheap labors due to their desperate conditions. During the war years of 1940, the federal government enacted the Bracero program in which many Mexican laborers were brought to US to work in agriculture on a temporary basis. Over the next two decades, almost 4.8 million Mexican workers entered into US and worked for lesser wages. Since 1990, it is estimated that the illegal immigrations outnumbered the legal entries and the inhabitants of undocumented foreign born persons in US has increased rapidly very year.
After September 11 2001 calamity, the US government increased the responsibility of Border Patrol to put in force more restrictions on illegal immigrations and also gave more authority to Homeland Security. In 2003, the Immigration and Naturalization Service (INS) was dissolved and absorbed into Homeland Security with the main focus on expelling and deporting unauthorized immigrants back to their own countries. Despite these efforts, according to the statistics of the Pew Hispanic center (PHC), the number of illegal immigrants that lived during the period of 2005 range between 11.5 to 12 million. By the end of 2009, as per the US department of Homeland Security estimation, Mexico is rated as the top most country to send nearly 12 million immigrants to US from 2000 to 2010 accounting for 29% of total immigration.
The illegal immigrations not only impacted the government and community but also had a great influence on US economy, wage and employment, crime rate and national security. In spite of spending 40 billion dollars in 2010 to deport 400,000 illegal aliens back to their countries, intensifying the immigration status checks of the various workers and enforcing laws for the detention of immigration violators, most Americans believe that United States is not doing enough to keep illegal immigrants coming into the country.