(Growth of Prison Population) "The prison population began to climb in the late 1970s as states and the federal government cracked down on crime. One turning point was New York State’s 1973 imposition of mandatory sentencing laws for drug offenses, under the administration of Gov. Nelson Rockefeller.40 Other states followed. Initiatives included mandatory sentences for repeat armed career criminals. Congress, in the Sentencing Reform Act of 1984 (18 U.S.C. 3651), repealed federal courts’ authority to suspend criminal sentences and made other changes.41 In 1994, California voters and legislators approved Proposition 184, the so-called Three Strikes Law. Among other things, the law set a minimum sentence of 25 years to life for three-time offenders with prior serious or violent felony convictions.42"

Source

Kirchhoff, Suzanne M., "Economic Impacts of Prison Growth," Congressional Research Service, (Washington, DC: Library of Congress, April 13, 2010), p. 7.
http://www.fas.org/sgp/crs/mi…