Did you bother to actually read the article? Chicago, or even Illinois, did nothing illegal or official to institute segregation. De Jure segregation isn't illegal. PRIVATE developers put clauses in their deeds and people who WANTED to be segregated bought into those neighborhoods. Many people refused to participate and did not buy from those developers. People tend to live with other people who reflect their views and appearance, we have hundreds of thousands of years of evolution conditioning us to do so.