Disunion follows the Civil War as it unfolded.

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When did the Civil War end? Many have answered never. As late as 1949, in an address at Harvard, the writer Ralph Ellison said that the war “is still in the balance, and only our enchantment by the spell of the possible, our endless optimism, has led us to assume that it ever really ended.”

Still, there was an ending of sorts, in 1865. Sometimes, it came cleanly, as with Gen. Robert E. Lee’s surrender at Appomattox on April 9. At other times, the war just seemed to give out, as soldiers melted away from their regiments and began to find their way home. Other generals in more distant theaters fought on gamely: Not until June 23 did Stand Watie, a Cherokee chief and a Confederate brigadier general, sign a cease-fire agreement at Doaksville, in what is now Oklahoma. The last Confederates of all were the furthest away: After evading capture in the North Pacific, the confederate raider Shenandoah sailed all the way to Liverpool, where its crew surrendered on Nov. 6, the fifth anniversary of Lincoln’s election.

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Then there was Abraham Lincoln’s assassination. This sickening act of violence, when added to all the others, brought a definitive feeling that an era had ended, as surely as Lincoln’s election in November 1860 had precipitated it. The funeral train that carried Lincoln’s remains home to Springfield, Ill., drew millions, and while the tragedy felt senseless, it also offered the nation a chance to mourn something much larger than the death of a single individual. To the end, Lincoln served a higher cause.

After he was laid to rest, on May 4, the armies united for an epic display of glory, worthy of Rome. Over two days, on May 23 and 24, more than 150,000 soldiers marched down Pennsylvania Avenue in Washington before a reviewing stand where President Andrew Johnson and Lt. Gen. Ulysses S. Grant stood.

That was a political as well as a military statement, for this vast army did not exactly disappear. The Grand Army of the Republic, founded in 1866, would become a potent lobbying force for veterans. Its immense gatherings helped to choose Lincoln’s successors for decades.

More than a year later, on Aug. 20, 1866, President Johnson proclaimed that final pockets of resistance in Texas were “at an end.” We could call this, too, the close of the war.

But much remained “in the balance,” as Ellison said; uncomfortable, unfinished. Certainly, the presence of so many veterans was a new fact for Americans, and kept the war alive, simmering, for decades.

More than a few required help to cope with their trauma, and the federal government, which had grown so much during the war, grew again to address their needs. It paid out pensions, it built hospitals, it maintained service records, and it assumed more responsibility for the mental and physical health of those who had given so much. That was an important precedent for the New Deal and the Great Society.

To this day, as a recent Wall Street Journal article reported, an elderly North Carolina woman, Irene Triplett, collects $73.13 a month for her father’s pension. He served in both the Confederate and Union armies: His tombstone avoids that complexity by saying simply, “He was a Civil War soldier.”

Reintegrating these former soldiers took decades. What we now regard as the best Civil War fiction, such as the work of Stephen Crane and Ambrose Bierce, did not even appear until the 1890s, as if the war’s memory was too potent at first.

A new product, Coca-Cola, was introduced in 1885 by a former Confederate officer, John Pemberton, who had been slashed by a saber in the final fighting of the war, after Appomattox, then wrestled with an addiction to morphine, to dull the pain. A pharmacist, Pemberton experimented with a mysterious formula that derived from the coca leaf and the kola nut, to ease his suffering. The early marketing for the elixir suggested that it could reduce the symptoms that veterans suffered from, including neurasthenia, headaches and impotence.

Many veterans retained their sidearms, including Confederate officers, and weapons were easily available, thanks to an arms industry that had done great service to the Union cause. They could hardly be expected to voluntarily go out of business. With new products (like Winchester’s Model 1866 rifle), sophisticated distribution networks and a public eager to buy, the industry entered a highly profitable phase. Winchester’s repeating rifles needed hardly any time for reloading, and sold briskly in Europe, where American arms tipped the balance in local conflicts.

The Winchester was easily transported to the West, where new military campaigns were undertaken against Native Americans, and few could be blamed for wondering if the Civil War had in fact ended. Many of the same actors were present, and it could be argued that this was simply another phase of the crisis of Union, reconciling East and West, rather than North and South.

This tragic epilogue does not fit cleanly into the familiar narrative of the Civil War as a war of liberation. Peoples who had lived on ancestral lands for thousands of years were no match for a grimly experienced army, eager to occupy new lands, in part to reward the soldiers who had done the fighting.

Natives called the repeating rifles “spirit guns,” and had no answer for them. They fought courageously, but in the end had no choice but to accept relocation, often to reservations hundreds of miles away. Adolf Hitler would cite these removals as a precedent for the Nazi concentration camps.

In other ways, the war endured. The shift westward created a huge market for building products, furnishings and all of the technologies that had advanced so quickly during the fighting. One skill that amazed observers was the speed with which Americans could build railroads and the bridges that they needed to cross. Between 1865 and 1873, more than 35,000 miles of tracks were laid, greater than the entire domestic rail network in 1860.

This activity was very good for business. Huge profits were made as those who had become wealthy supplying the war effort adapted to the needs of a civilian population eager to start anew. Indeed, it is difficult to tell from the 1870 census that any war had taken place at all. The 1860 census had valued the total wealth of the United States at $16 billion; 10 years later, it was nearly twice that, $30 billion. So many immigrants came between 1860 and 1870 that the population grew 22.6 percent, to 38.5 million, despite the massive losses of war dead.

To careful observers in 1865, it was palpable that something important had already happened during the war. To organize victory, a grand consolidation had taken place, in which leading concerns had improved their organizations, crushed their smaller rivals and strengthened distribution networks. The railroad was a key part of this consolidation; so was the telegraph, often built along the tracks. Military goods needed to move quickly around the country to supply armies, and all of those skills were instantly transferable to private enterprise. One firm, an express freight delivery service founded in Buffalo, moved its goods slightly faster than the competition. It was, and is, known as American Express.

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Information was vital to make all of these systems work. During the war, the Military Telegraph Corps built 8 to 12 miles of telegraph line a day; and the military alone sent 6.5 million messages during the war. By the end of 1866, more than 80,000 miles of line existed, and these were rapidly extended into the West and South, reknitting some of the strands of Union.

Entirely new sectors of the economy had sprung up as well. In 1859, on the eve of the conflict, oil was discovered in northwestern Pennsylvania, and throughout the war, its value became clear to a war economy that urgently needed to lubricate the machinery of production. John D. Rockefeller bought a refinery in Cleveland in 1863, a major step on the way to the creation of Standard Oil. As soon as the war ended, the search for oil in new locations began: The first well in Texas was dug in 1866, in Nacogdoches County.

Many veterans, having paid so dearly for freedom, were troubled to come back from the war, only to find a new economy, dominated by industrial barons, quite a few of whom had paid substitutes to do their army service. Lincoln’s words about freedom continued to move people, but his emphasis on equality seemed to fade as the power of money rose to new heights. It was not only that a small elite had become extremely wealthy; but money itself seemed to move in new ways, fast and loose.

In other words, it was unclear to many Americans what, exactly, they had won. A great evil had been defeated; and Union forcibly defined and defended. But so rapid were the changes unleashed by the war that soldiers blinked their eyes in amazement when they returned home. Like Ulysses, the Greek hero their commander was named after, they often did not recognize the country they came back to.

Perhaps the most complicated legacy of the war was its claim to have liberated millions of African-Americans from slavery. This was not the official purpose of the war when it began in 1861, but it became so, especially after the scale of the war required a cause worthy of so great a sacrifice.

But when did slavery actually end? Was it the national ratification of the 13th amendment, on Dec. 6, 1865? Or the day Mississippi ratified it, in 1995? Or the gift of full citizenship (including voting rights) to African-Americans? There are those who would argue that we are still waiting for that Day of Jubilee. To read the stories that came out of Ferguson, Mo., Cleveland and Baltimore in the last year — all communities that remained in the Union — is to realize how distant the victory of the Civil War feels to large numbers of African-Americans.

Of course, that does not minimize the importance of the Confederacy’s defeat. It ended forever a way of life and politics that had dominated the United States from its founding. It accelerated the demise of slavery where it still existed, in Cuba and Brazil, and encouraged liberals around the world to push for greater rights. In the fall of 1865, Victor Hugo wrote in a notebook, “America has become the guide among the nations.”

In France, Napoleon III was destabilized by Lincoln’s victory, and pulled back from his adventure in Mexico, where his puppet, Maximilian, was shot by a firing squad in 1867. Three years later, he was removed after his defeat in the Franco-Prussian War, and the transfer of the provinces of Alsace and Lorraine to Germany left a bitterness that would fuel the world wars of the 20th century.

Without the Civil War, and its tempering of the national character, would the United States have been able to mount a great global campaign against fascism? Surely it would have been feebler, without the manufacture of war matériel across all the regions, or the rhetoric of freedom Franklin D. Roosevelt used to inspire the world.

Nearly all of the national triumphs of the last century, from the civil rights movement to the exploration of space to the birth of the digital age, stemmed from the contributions of Southerners, Northerners and Westerners working together. We have had failures too — we see them on a daily basis. But the refusal to fall apart in 1861 made a difference.

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Ted Widmer is an assistant to the president for special projects at Brown University, and the editor of “The New York Times Disunion: Modern Historians Revisit and Reconsider the Civil War from Lincoln’s Election to the Emancipation Proclamation.”

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