The Civil War was not originally framed as a war to free the slaves. Like Lincoln's facial hair over the years, it changed as it went along.
In its early years, President Lincoln promised not to impose abolitionist goals on the South. He might have had his fingers crossed behind his back on that one, but he was desperate to keep border states like Kentucky and Maryland loyal to the Union. He believed that making the war explicitly about slavery would make this difficult, so he told them what they wanted to hear. We wonder if Mary Todd ever got the same treatment.
Lincoln wanted to keep as many people on his side as he could, so it wasn't until September 22, 1862 that Lincoln proposed to free the slaves. Now there's a proposal that would have gotten over 10,000,000 hits on YouTube.
Even then, Lincoln issued only a provisional proclamation to emancipate slaves in select parts of the South where he technically had no authority and no way to enforce it anyway. As the war had increased in violence, it became clear that the South was not going to stop fighting and peacefully rejoin the Union, no matter how many gift cards and coupon booklets Lincoln offered them. Lincoln was not above bribery.
After the bloody Union victory at the Battle of Antietam in 1862, Lincoln issued an ultimatum: he threatened to order slaves freed in all areas of the Confederacy that failed to declare loyalty to the Union by New Year's Day. So much for a little R&R over the Christmas holiday.
Unfortunately for the South, Lincoln never bluffed. On January 1, 1863, he issued his famous Emancipation Proclamation, effectively freeing slaves in those parts of the South that remained hostile to the Union. In many ways, however, the Proclamation was limited. It didn't expressly free slaves in loyal border states, and it exempted those areas of the Confederacy already under Union control. Baby steps, right?
The fact is that Lincoln's ultimatum didchange the character of the war in fundamental ways. After the Proclamation, the war became, for the North, a conflict aimed at freeing the slaves and ending the southern planter aristocracy. They wanted to "uproot" the planters, if you will. (You might as well—we already did.)
Each advance of northern troops was now a move for freedom. Each town and farm captured now aided in the emancipation of slaves. What had begun as a war to corral rebellious states had suddenly become a great crusade for freedom and liberty, and that got the Union troops pumped up and ready to keep fighting. Liberty does that to people. That big, old green statue was smiling down on them.
The Emancipation Proclamation also turned the war into even more of a fight to the death than it already was. The South knew that losing the war now meant an end to life as they knew it before the war.
Additionally, Lincoln allowed black soldiers to fight for the Union. The Confederacy didn't follow suit until the very last months of the war, when they had gotten uber-desperate for men. They also promised to shoot any captured black Union soldiers as runaways, but that didn't deter over 200,000 black men from fighting for the Union.
It wasn't all Equality City for black Union soldiers, though. The most famous black unit was the 54th Massachusetts Infantry, led by a white colonel named Robert Gould Shaw. (All black units were commanded by white officers, kind of like in the NBA.) Sure, they got to be soldiers, but many of the black units were forced to perform menial tasks in support of white fighting units and, until late in the war, were paid at a lower rate than white troops, if at all. Some of them weren't even paid in Trident Layers. Despite the prejudice they experienced, units like the 54th fought bravely and successfully in many battles. Take that, injustice.
Though the North fought the war to abolish slavery, not everyone there had boarded the agreement train to Happytown. There was still tons of racism in the North, and it occasionally provoked serious violence. The most famous instance was the series of draft riots in New York following the beginning of conscription in July 1863. These were nothing compared to the NFL Draft Riots of 1982, during which Marcus Allen was given a particularly vicious noogie.
Fearing that a free black population would take their jobs, many working-class groups, particularly the Irish, grew resentful of the war. Ultimately, they rebelled against the draft, or the O'draft, as they probably called it.
The four day riots that ensued were about many things—including the decision to allow rich men to pay their way out of fighting in the war ("Hey, you get back here and die with the rest of us!")—but race lay beneath it all. Bands of Irish workers and others sought out blacks living in the city and attacked them. It was not cool. Over 200 men, women, and children were killed before Union soldiers returning from Gettysburg ended the mayhem. The war ended slavery, but it did little to end the prejudice and racism that blacks faced in the North as well as in the South. On the upside, well…there really was no upside. Sorry to end on a downer.