Two months before President Lincoln presented the Emancipation Proclamation to his cabinet in July 1862, it seemed the Civil War was about to end with slavery essentially intact. Union armies were trouncing Confederate forces on nearly every front: the Navy had reclaimed much of the Mississippi River; New Orleans, Nashville and Memphis had fallen; and U.S. troops occupied the coastal islands of South Carolina. In Tennessee, General U.S. Grant had won the biggest battle in the war so far at Shiloh. Meanwhile in Virginia, General George McClellan’s Army of the Potomac had turned Confederate forces out of Yorktown, hit them hard at Williamsburg, and was now rapidly closing in on the Confederate capital at Richmond. With the Rebels apparently falling back to their last ditch, the New York Herald optimistically claimed that Union forces were poised to deliver “the coup de grace to this rebellion.” The New York Times concurred: “Richmond is doomed, and everybody knows it,” the paper declared on May 19. “This week, it is thought, will . . . pour utter ruin on the Confederacy.” If these bold predictions proved accurate, the war might end with millions of African Americans still enslaved.

These predictions did not prove true, however, because on June 1, 1862, General Robert E. Lee took command of the Army of Northern Virginia. Ironically, that appointment was a key factor in changing the equation that had, until then, protected slavery.

For months, radical Republican congressmen had been trying to avoid a scenario in which the war ended with slavery intact. They had pushed for legislation that would allow the military to confiscate and free all slaves owned by Confederates. Deeming the measure a “military necessity,” they insisted that slavery was a source of Confederate strength because the Rebels forced slaves to build entrenchments and fortifications. Additionally, the radicals argued that if the United States were to free the slaves, it would take a strength away from the Confederacy and add it to the Union.

But the U.S military’s successes in early 1862 made these arguments highly debatable. With the war apparently about to be won, Democrats and many conservative Republicans resisted efforts to pass a confiscation bill that seemed increasingly unwarranted. “Our armies and navies are victorious, Massachusetts representative Benjamin F. Thomas told Congress in May, “The war seems to be drawing to a close. There is reasonable ground to hope that [soon] the power of this rebellion will be broken.” Despite such strong opposition, the radicals fought on, all the while fearing Lincoln would not sign the legislation even if they managed to pass it.

Lincoln’s antislavery sentiments were not in doubt. Although insisting the war’s sole objective was the Union’s preservation, he had long denounced slavery. He had also recently supported several emancipationist endeavors; the prohibitions of slavery in Washington DC and in the western Territories, as well as a treaty with Britain to suppress the international slave trade more effectively. Most dramatically, Lincoln was pressuring the Border States to accept compensated emancipation and had secured funds from Congress to do it.

Unfortunately for the radicals who wanted a confiscation law to end southern slavery, however, as McClellan neared Richmond none of the president’s actions demonstrated he supported attacking slavery in the seceded states. In fact, his efforts were consistent with longstanding positions: the government should stop the spread of slavery, it should cease using federal power to sustain the institution, and it should encourage compensated emancipation. Aside from those actions, the national government could not touch slavery in the southern states. Northerners elected Lincoln on this platform in 1860 and he strayed little from it during his first fourteen months in office. Radical measures, he feared, might doom his compensated emancipation scheme, destroy any Union sentiment in the southern states, and drive the Border States into rebellion.

This cautiousness infuriated abolitionists and congressional radicals, especially when the president seemed to undermine their arguments in support of their confiscation bill. In early May, an old friend of Lincoln’s, General David Hunter, took the bold if politically naïve step of declaring that all the enslaved persons within his military jurisdiction (which included South Carolina, Georgia, and Florida) were “forever free.” Radicals praised the action, taking heart when Secretary of the Treasury Salmon P. Chase made it known that he supported Hunter’s decree, telling Lincoln it was of the “utmost importance” that he not revoke the order because it would strengthen the radical position. Lincoln’s response was terse: “No commanding general shall do such a thing, upon my responsibility, without consulting me.”

On May 19, Lincoln declared Hunter’s emancipation order “altogether void,” warning other commanders not to make a similar mistake. Many considerations led to this decision, not the least of which was the swift denunciations it received from the Border States Lincoln was trying to woo into compensated emancipation. Obviously, he also could not allow military commanders to create policy, especially on such a weighty issue. Yet Lincoln also publicly declared it was solely his responsibility to determine “whether at any time . . . it shall have become a necessity indispensable to the maintenance of the government” to liberate slaves in the seceded states. He made it clear that he felt that time had not arrived, seemingly siding with the confiscation bill’s opponents. With all the military’s successes, and especially with the Army of the Potomac arriving only eight miles from Richmond, why should he feel otherwise?

By the last week of May, it became obvious to congressional radicals that with the current military situation they were unlikely to get a bill passed that would emancipate any slaves. Further, Lincoln’s response to Hunter demonstrated that he might not sign any such legislation. He did not yet agree that freeing slaves was a military necessity, making it clear that if that moment ever did come, it was his decision alone. On May 26, the House rejected a bill that would have emancipated all slaves whose masters were in rebellion.

The legislation did not die, however. Republican leaders sent it back into committee. With Union armies successfully advancing on almost all fronts, and as McClellan’s army prepared to assault the Confederate capital, supporters of the confiscation bill were losing the argument that emancipation was a military necessity. Added with Union military successes elsewhere, if McClellan captured Richmond the war might end, Lincoln would resume his gradualist approach toward strangling slavery, and as the radicals feared, the opportunity to free the slaves as a war measure would be lost.

Nevertheless, Salmon Chase felt Lincoln was still grappling with the issue, and in June suspected that a “contingency” could force the president to accept that emancipation was a military necessity. “My conviction,” he wrote to General Ben Butler “is that that contingency will soon arrive.”

On June 1, Confederate President Jefferson Davis placed Robert E. Lee in command of the Army of Northern Virginia, and this promotion helped bring about the “contingency” that changed Lincoln’s mind about emancipation. At the end of the month (and just two days after Chase’s prediction), Lee launched his first campaign against the Federals, aggressively attacking and driving them away from Richmond. This success (followed by more Rebel victories) stunningly revived the fortunes of the Confederacy, instantly gave credence to the military necessity argument, and thus ironically doomed the institution of slavery. The confiscation bill soon passed, Senator Charles Sumner explained, because of political “pressure from our reverses at Richmond.”

More importantly, as Secretary of the Navy Gideon Welles related, in mid-July Lincoln concluded “that it was a military necessity absolutely essential for the salvation of the Union, that we must free the slaves or be ourselves subdued.” Much to Chase’s satisfaction, on July 22 the president announced to the cabinet his intention to issue the Emancipation Proclamation.

It was a stunning shift, demonstrating how quickly and effectually military events could alter government policy and the course of the Civil War. Just two months after Lincoln chastised Hunter, Robert E. Lee’s successes helped convince the president that saving the Union required emancipation, ensuring the war would deal slavery a fatal blow.