Racial steering refers to the practice in which real estate brokers guide prospective home buyers towards or away from certain neighborhoods based on their race. The term is used in the context of de facto residential segregation in the United States, and is often divided into two broad classes of conduct: Advising customers to purchase homes in particular neighborhoods on the basis of race. Failing, on the basis of race, to show, or to inform buyers of homes that meet their specifications. Historically the United States of America has been defined by racially segregated neighborhoods. Urban planning up to the 1960s has been documented as one of the causes of this phenomenon. Urban planners have been seen to have practiced early forms of racial steering. Through the use of the restrictive covenant, and the establishment of zoning laws between World War I and World War II, and the use of urban renewal between the 1940s and 1960s, urban planners have aided in the development of racially segregated neighborhoods. After the 1960s, through in part by the Civil Rights Movement, planning efforts were focused more towards advocacy, and community development, rather than maintaining segregation. Although planning practices did change, the racial make-up of neighborhoods did not. Researchers have attempted to explain the racial segregation seen in neighborhoods throughout the United States. There are three leading theories. The first "asserts that the phenomenon is really self – segregation, the result of the preferences of blacks, as with other ethnics, to live in segregated neighborhoods. The second suggests that poverty, aided by the inertia of history has perpetuated segregation. The third suggests that the decline of blatant discrimination of the past has revealed pervasive institutional racism." John E. Farley, argues that although it is plausible for each of these theories to contribute to the segregation seen, his research lends the most support to the second theory, which bases itself on social class.