When and why did the Immigration and Naturalization Service (INS) change to the U.S.Citizenship and Immigration Services(USCIS)?

(Referenced from: http://www.immigration.gov)

On March 1, service and benefit functions of the U.S. Immigration and Naturalization Service (INS) transitioned into the Department of Homeland Security (DHS) as the U.S. Citizenship and Immigration Services (USCIS). The President nominated Eduardo Aguirre to lead the USCIS; he was confirmed by the Senate on June 19, 2003. The USCIS is responsible for the administration of immigration and naturalization adjudication functions and establishing immigration services policies and priorities.

These functions include:
- adjudication of immigrant visa petitions;
- adjudication of naturalization petitions;
- adjudication of asylum and refugee applications;
- adjudications performed at the service centers, and
- all other adjudications performed by the INS.