In terms of how segregation was maintained legally, the use of the Jim Crow laws in the South did much to ensure that two worlds were maintained. Jim Crow Laws in the South ensured that white culture and the African- American culture would remain distinct in as many ways as possible. The preservation of "states' rights" in the South became synonymous with segregation. Jim Crow laws in the South were matched by zoning laws and municipal codes in the North that ensured that people of color were denied equal access and opportunity in as many realms as possible.
[The] implications of early [Los Angeles] zoning initiatives ... [were such that] "What began as a means of improving the blighted physical environment ... for protecting property values and excluding the undesirables" (Yale Rabin) ... as the undesirables were immigrants and African Americans. (Christopher Silver, The Racial Origins of Zoning in American Cities)
The use of the legal conditions to ensure that segregation was maintained was vitally important in preventing integration until the 1950s. The use of the law, which had not adapted itself to the reality of Civil Rights, was one way in which segregationists found authority.
In terms of illegal activity, the use of intimidation in as many realms as possible was critical to segregationists being able to ensure their control prior to integration. The use of lynchings, beatings, and murders were all part of this activity These were practices through which segregationists were able to assert control over people of color prior to an integrated nation.
Segregation was maintained by different means in the North and South, some legal, others "extra legal." The primary difference between the two is that segregation in the South was sanctioned by law, so called de jure segregation. State statutes provided that schools and public facilities be segregated, and made it illegal for Black citizens to enter any establishment with a sign indicating it was for "whites only." Blacks were often prevented from serving on juries by having cards from which jury members were drawn color coded by race, so that only white jurors were drawn. Illegal methods primarily consisted of intimidation and threats which were largely ignored by law enforcement.
Segregation in the North was not pursuant to statute, but did exist. This type segregation was known as de facto segregation; that is segregation in fact. This was normally maintained by refusing to do serve or accommodate black persons in places of business, "African descent" clauses in real estate restrictions or deeds, and "white flight," in which white families often moved away from neighborhoods where blacks lived. The end result was the same as in the South, but was not pursuant to law.