Given the following passage  "On August 18, 1970, the NAACP filed suit against Michigan state officials, including Governor William Milliken, charging de facto public school segregation. The NAACP argued that although schools were not legally segregated, the city of Detroit and its surrounding counties had enacted policies to maintain racial segregation in public schools. The NAACP also suggested a direct relationship between unfair housing practices and educational segregation, which followed segregated neighborhoods. The District Court held all levels of government accountable for the segregation in its ruling. The Sixth Circuit Court affirmed some of the decision, holding that it was the state's responsibility to integrate across the segregated metropolitan area. The U.S. Supreme Court took up the case February 27, 1974. The subsequent Milliken v. Bradley decision had wide national influence. In a narrow decision, the Court found that schools were a subject of local control and that suburbs could not be forced to solve problems in the city's school district.",  answer the following question. Note that the answer is present within the text.  Question: What was the basis of the beef that the NAACP had?
Answer:
the city of Detroit and its surrounding counties had enacted policies to maintain racial segregation in public schools