The American Civil War could have ended without the abolition of slavery. Such an outcome is difficult to imagine because Americans tend to frame the end of slavery as part of the nation's inevitable march toward greater freedom. The Civil War somehow seems incomplete without it, but at any point before 1863 the surrender of Confederate armies would have signaled the end of the Rebellion and reunion. Far from inevitable, slavery unraveled slowly through congressional legislation, presidential proclamation, military necessity, and the initiative taken by countless slaves throughout the South. Few people could have predicted in 1861 that in a few short years four million bodies, worth more than all the commercial and manufacturing assets in the nation combined, would be freed.

One hundred and fifty years ago today, on December 6, 1865, the state of Georgia became the 27th state to ratify the 13th Amendment. The state’s ratification took place close to a year following the vote on the amendment in the House of Representatives on January 31, 1865, the subject of Steven Spielberg’s Oscar-winning film Lincoln. In a scene following the dramatic House vote, abolitionist Republican Congressman Thaddeus Stevens, played brilliantly by Tommy Lee Jones, walks through the streets of Washington, D.C. amidst the sounds of church bells and cheering crowds with the original copy of the amendment in hand. Audiences were no doubt surprised to follow Stevens home only see him climb into bed with Lydia Hamilton Smith, his life partner for 20 years, whom the public understood to be his black housekeeper.

It is a poignant moment. The two lie next to one another as Smith reads out loud the words that effectively outlawed slavery forever in the United States. Those words represent the crowning achievement of the Civil War for many Americans, but most moviegoers likely gave little thought to Smith's reading of Section 2 of the amendment, which gave Congress the “power to enforce this article by appropriate legislation.” Unlike previous constitutional amendments that curtailed federal power, Section 2 expanded the reach of the federal government. For former Confederate states now taking part in the ratification process—a process that required 27 of 36 states to vote in its favor—the threat of federal enforcement was a major concern as they struggled to salvage white supremacy from the painful reality of defeat and emancipation.

The decision to include an enforcement clause stemmed from an oversight in the Northwest Ordinance of 1787, which every student of AP United States history knows barred slavery from the territories north of the Ohio River. While it succeeded in pushing out many slaveholders from the region, those who stayed soon learned that the ordinance had no teeth. It could not be enforced. In fact, at one time slaveholders occupied the governor’s chairs in the new states of Illinois and Indiana. In 1820, census takers counted 917 slaves in Illinois and 190 in Indiana. It took another 25 years for Illinois to comply with the terms of the Northwest Ordinance. Diehard Confederate resistance no doubt convinced Republican authors of the 13th Amendment that the defeated slave states would only comply with a constitutional amendment ending slavery if it came with an explicit enforcement clause.

But what authority did Congress give itself to enforce the 13th Amendment? Was it to be interpreted broadly or narrowly, and did it extend beyond simply ensuring that former slaves were not being bought or sold to include full civil rights? These questions were hotly debated by state legislatures between February and December 1865.

Strong Republican states that awarded President Abraham Lincoln with a second term in office in 1864 voted overwhelmingly for the amendment in the first weeks of February. The first signs of trouble occurred in the “Border States” of Delaware and Kentucky as well as New Jersey. Delaware was one of four Border slave states that remained in the Union, and its slave population amounted to no more than 1,200. But Democrats in the state legislature weren’t concerned about abolition. Their worries centered around how the federal government might interpret the provisions of the enforcement clause and based on that interpretation, just what the government might then force the states to do beyond ratifying an amendment ending slavery. Gov. Gove Saulsbury spoke for many in his state when he argued that the "Black Republicans" would next "demand for the negro the right of suffrage, and seek to place him, politically at least, upon an equal with the white man." Shortly thereafter, the amendment came up for debate for the second time in Kentucky, where not even a provision calling for federal compensation to slaveholders and the removal of every black person could marshal sufficient support.

Even in the free state of New Jersey, where the amendment failed in a close decision after legislators voted strictly along party lines, similar fears among Democrats concerning "amalgamation" and "negro equality" surfaced over the enforcement clause. The views expressed in New Jersey and the Border States point to a widespread fear among white Americans surrounding the implications of abolition. Americans applauded the end of slavery as necessary to win the war, as a way to strengthen the Union, and as punishment to the leaders of the rebellion, but that did not mean that they were prepared to elevate African Americans socially or politically.

Ironically, it was the concerns expressed by former slave states during the ratification process that spoke for many of the fears expressed by white Americans, North and South. By July 1, 1865, 23 states had voted for ratification, just four shy of the number needed for the amendment to be added to the Constitution. Only four former Confederate states, including Virginia, Louisiana, Tennessee, and Arkansas, had voted in favor of it. All complied with Democratic President Andrew Johnson’s lenient terms for readmission into the Union that included framing new state constitutions that abolished slavery, repudiating ordinances of secession as well as their war debt, and ratifying the 13th Amendment. But more votes to ratify were needed and fast.

As the summer progressed, many Southern states enacted Black Codes to regulate the conduct of former slaves. Former slaves were barred from owning firearms or alcohol, pursuing a trade, and even gathering in public places. Under these laws, petty criminals could be sold at auction. In South Carolina blacks were limited to working as farm laborers or domestic servants, while Mississippi's code prevented African Americans from owning or leasing farmland. The Black Codes attempted to return states as closely as possible to the antebellum status quo. Only the 13th Amendment’s enforcement clause prevented these states from closing that gap completely.

The public saw very little activity on the ratification front throughout much of the summer and fall. Behind the scenes, however, President Johnson was working to get the amendment through South Carolina’s state legislature—the birthplace of secession and rebellion—but even in defeat the state remained defiant. Only the possibility of ending military occupation by the U.S. army propelled the debate forward. Lawmakers acknowledged the end of slavery in their new state constitution, but added that it had been forced on them, “by the actions of the United States authorities.” As for formal ratification of the 13th Amendment, the wording of Section 2, they believed could be “construed to give Congress power of local legislation over the negroes, and white men.”

Only after receiving reassurance from Secretary of State William Seward that the clause was “restraining in effects, instead of enlarging” the federal government’s power did the state agree to ratification, which it did on November 13. As a measure of reassurance a proviso was attached stating, “That any attempt by Congress towards legislating upon the political status of former slaves, or their civil relations, would be contrary to the Constitution …” Shortly thereafter Alabama ratified the 13th Amendment, but with the “understanding that it does not confer upon Congress the power to legislate upon the political status of Freedmen in this State.” Two days later North Carolina followed suit.

Finally, on December 6, 1865 the state of Georgia sent the amendment over the edge to victory. Four years earlier the newly elected Confederate Vice President from Georgia, Alexander Stephens, addressed a crowd in Savannah on the “cornerstone” of their new government. “Our new Government,” asserted Stephens, “rests upon the great truth that the negro is not equal to the white man; that slavery, subordination to the superior race, is his natural and normal condition.” Now, even as the states took steps to abolish slavery, they rallied once more around this “great truth” and continued to do so for the next 100 years.

There is something curious about a country that zealously promotes itself as the world’s beacon of freedom and yet chooses not to celebrate the passage of the 13th Amendment as a national holiday. Perhaps part of the answer is contained in the fact that the process of ending slavery in this country and moving forward toward full racial equality involved both its resistance and embrace—a tug of war that we have yet to fully reconcile.

Kevin M. Levin is a historian and educator based in Boston. He is the author of Remembering the Battle of the Crater: War as Murder (2012) and is currently at work on Searching For Black Confederate Soldiers: The Civil War’s Most Persistent Myth. You can find him online at Civil War Memory and Twitter @kevinlevin.