The Age of Entitlement by Christopher Caldwell. The basic thesis is that the civil rights movement and apparatus created, de facto, a new constitution that was incompatible with the old one. The old constitution favored freedom, the new one favored equity. As he says:

Much of what we have called ‘polarization’ or ‘incivility’ in recent years is something far more grave. It is the disagreement over which of the two constitutions shall prevail: the de jure constitution of 1788, with all the traditional forms of jurisprudential legitimacy and centuries of American culture behind it; or the de facto constitution of 1964, which lacks this traditional kind of legitimacy but commands the near-unanimous endorsement of judicial elites and civic educators and the passionate allegiance of those who received it as a liberation.

Civil rights became a way of doing government and implementing policy. And this method was expanded well beyond the Jim Crow south; it was expanded into many other social struggles such as gay rights, affirmative action, and a whole host of other social struggles that many Americans did not imagine they were signing up for. A lot of the sense of polarization that has taken place since the 60s is because people had different ideas of what civil rights meant. A lot of white Americans felt embarrassed by the Jim Crow south, and backed civil rights as a means of correcting that one specific problem. But many civil rights activities saw things differently, in that they saw civil rights as a means of improving the station of first black people, and eventually everybody who was not a straight white man. Civil rights did not directly harm straight white men, but it was designed to help everybody except for them, which is the same thing. Case in point, take this article: https://www.axios.com/biden-personnel-team-opm-7df87473-3fd3-4ff7-9289-c89994e50879.html

Notice that reducing the number of white men to only 15% is framed as a good thing, and that the fewer white men there are, the more diverse an organization is. People notice these things. If you're a subscriber to the old constitution, you see this as a fundamental breech of fairness that violates the promise of the country. If you're a subscriber of the new constitution, you see this as a fulfillment of the promise of America since non whites and non men have been victimized and need to be lifted up. That conflict is the root of the country's division.