Reading the Articles of Secession passed by Southern legislatures in 1860, it soon becomes evident that Southerners “knew what they fought for and loved what they knew”: Negro slavery. It has been harder to fathom for what cause the Union fought. Was it to preserve the United States created by the Founders, regardless of emancipating the slaves? Was it to destroy slavery, a goal not well-articulated at first, but ever more clear in the minds of Unionists as the war dragged on? Elizabeth Varon argues that Union and Emancipation were subordinate causes to the larger goal of extirpating a poisonous social system that oppressed all but a few Southerners, slave or free, and threatened to destroy the “last, best hope of earth.” In this argument, slavery provided the solid foundation for a system that submerged in a sea of racism real conflicts between a small and powerful aristocracy and the vast majority of white Southerners. Varon argues that the Union armies were fired by a zeal that spilled over from and was enunciated in the language of the religious enthusiasm that marked mid-19th Century America. They saw themselves as Delivering the country from mortal peril. Thus, “lead us not into temptation, but deliver us from evil.”—Matthew, 6:13. “We bring the Jubilee!”—a Biblical reference in Henry Clay Work’s “Marching Through Georgia.” See: Leviticus, 25:8-13. In this sense, the victorious Union armies liberated their enemies as much as they did the slaves.
Or perhaps more than they did the slaves. Freeing blacks did not reconcile Southern whites to the Union. They rose up in a new rebellion, often taking the form of the Ku Klux Klan. During the decade after “the recent unpleasantness,” Northern enthusiasm for equal rights for blacks rapidly waned. Southern whites regained control of the political system, then began to create the legal structures for imposing inferior status on blacks. Of course, disfranchisement formed the cornerstone of this effort. However, a host of laws also sought as much segregation of the races as possible. A group of bi-racial New Orleans civic leaders tried to stop this juggernaut as it gathered speed. They sued to block a Louisiana law the required the separation of train passengers on the basis of race. Eventually, in 1896, the case reached the Supreme Court of the United States. The Court essentially adopted the position that the Constitution (and its amendments) is a living document. As such, jurists had to interpret its meaning to adapt the Constitution to changing times. The Court overwhelmingly endorsed the doctrine of “separate, but equal.” Only Justice John Marshall Harlan, apparently an originalist, insisted that the 14th Amendment meant what it said.
 See: http://www.civil-war.net/pages/ordinances_secession.asp
 Elizabeth Varon, Armies of Deliverance: A New History of the Civil War (2019).
 This seems to me to be an extension of the argument made by Edmund Morgan, American Slavery, American Freedom: The Ordeal of Colonial Virginia (1975).
 Steve Luxenberg, Separate: The Story of Plessy v. Ferguson and America’s Journey from Slavery to Segregation (2019).