The Civil Rights Act was the most important legal step to combat inequality taken in the United States since the three Reconstruction amendments were added to the Constitution in the 1860s. The Bill of the Century is the title of Clay Risen’s smart and stirring new history of the struggle to pass it, and one can’t really argue with that.

Yet the law’s significance lies as much in the battles that were waged over whether and how to enforce it as in the ways it changed American society for the better. In 1964, James J. Kilpatrick, a popular syndicated columnist, declared in National Review, “This precious right to discriminate underlies our entire political and economic system” and warned of perils to come. Fierce opposition to implementing the CRA was largely responsible for Lester Maddox’s election as governor of Georgia in 1966 and for George Wallace’s capture of 46 electoral votes two years later. Meanwhile, millions of whites from Southern and border states moved away from cities lest they and their children have to share public spaces and schools with black people.

All over the country, flashpoints emerged over Title VII of the Act, which prohibits employers from discriminating against employees based on race, religion, sex, or national origin. Right after the law was passed, as Nancy MacLean describes in her indispensable book, Freedom Is Not Enough, workers of different races and both genders began putting it to the test. Grievances from black painters, Mexican-American postal workers, and white airline stewardesses flooded into the offices of the new Equal Employment Opportunity Commission (EEOC), which the 1964 Act had created. During the EEOC’s first year, women lodged more complaints related the “loss of jobs due to marriage or pregnancy” than to any other issue related to sex discrimination (as it was then called). The National Organization for Women, founded in 1966, first made a name for itself when it petitioned the EEOC to ban want ads segregated by gender.