How were blacks segregated in northern cities?

Jim Crow laws were state and local laws that enforced racial segregation in the Southern United States. All were enacted in the late 19th and early 20th centuries by white Democratic-dominated state legislatures after the Reconstruction period. The laws were enforced until 1965. In practice, Jim Crow laws mandated racial segregation in all public facilities in the states of the former Confederate States of America and other states, starting in the 1870s and 1880s. Jim Crow laws were upheld in 1896 in the case of Plessy vs. Ferguson, in which the U.S. Supreme Court laid out its "separate but equal" legal doctrine for facilities for African Americans. Moreover, public education had essentially been segregated since its establishment in most of the South after the Civil War

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Explanation:

in griswold v. connecticut (1965), the supreme court ruled that a state's ban on the use of contraceptives violated the right to marital privacy.