On this day in 1862, Congress passed an article of war forbidding Union Army personnel from returning fugitive slaves to their masters. There have been several discussions on this site about whether or not the Civil War erupted over the issue of slavery. The editorial position of the EotAW is that the answer is, “yes.” And yet, the preceding is a very different argument than claiming that Union soldiers fought, either at the behest of their leaders or because of personal preferences, to free the slaves (though Chandra Manning has recently made precisely this point).

In other words, I follow Jim McPherson’s lead, arguing that the war began because southern slaveholders demanded that the peculiar institution be allowed to spread westward and take root in free soil. In the run-up to and then after winning the 1860 election, Lincoln, by contrast, always insisted that containing slavery was the bedrock principle on which the Republican Party rested, the one issue about which there could be no compromise. Slaveholders refused to accept this. South Carolina seceded. The rest of the Confederacy followed. And Lincoln chose to fight for the Union.

Again, though, constraining slavery’s spread and preserving the Union are different goals from abolition or even gradual emancipation, neither of which Lincoln pursued early in the war. Which is to say, slavery’s fate was the Civil War’s root cause, not African-American freedom or anything like black equality. But on this day, in 1862, the federal government took a big step toward shifting its war aims: from restoring the Union and keeping slaves out of the West to destroying slavery outright.

Before March 13, 1862, the Union Army had no clear policy for how to handle so-called contraband slaves. As a result, officers treated slaves that crossed the lines seeking shelter or the opportunity to fight for their freedom on an ad hoc basis. Benjamin Butler, for example, had refused, the previous summer, to return contraband slaves to the whites who claimed them. But other commanders had followed the dictates of the noxious Fugitive Slave Law, forcing contraband slaves back into servitude. That practice, in turn, had enraged radicals in Congress, abolitionists especially, who finally pushed through the article of war making it a crime, punishable by court-martial, to return contraband slaves to their owners.

Lincoln’s views on slavery, meanwhile, slowly shifted. He rode political currents, recognized the strategic value of freeing the slaves, and began grappling with ethical dilemmas about liberty. In sum, though hardly a radical, he embraced emancipation.

Around this time in 1862, he asked Congress to offer incentives to states that would move toward freeing their slaves. He still justified this request not on moral grounds but by suggesting that compensated emancipation would shorten the war, saving the lives of northern troops: by robbing the South of labor and, perhaps, enticing the border states, once their slaves had been freed, back into the Union. The law passed. But it didn’t work. Lincoln’s emancipationist sentiment, though, deepened as time passed. Until, the following fall, he decided to issue his Emancipation Proclamation, a document that was, it should be said, rather weak tea. Still, that ending slavery was one of the Union’s war aims never again would be in doubt after January 1, 1863, the end of an evolution that can, at least in part, be traced back to this day in 1862.