From Wikipedia's "List of Common Misconceptions"
According to Time magazine, there is a common misconception among Americans that Abraham Lincoln freed the American slaves with the Emancipation Proclamation of January 1863. Flagging fortunes in the spring and summer of 1862 brought the threat of European intervention on behalf of the Confederacy. Lincoln argued that turning a fight to crush rebellion into a crusade against slavery would not only end the European threat, as no Continental power would want to be seen supporting slavery, but would also sway abolitionists into supporting the administration. Slaves were not immediately freed as a result of the Proclamation, as it only applied to rebelling states not under Union control. Additionally, the proclamation did not apply to parts of rebelling states already under Union control. The Proclamation did not cover the 800,000 slaves in the Union's slave-holding border states of Missouri, Kentucky, West Virginia, Maryland or Delaware. As the regions in the South that were under Confederate control ignored the Proclamation, slave ownership persisted until Union troops captured further Southern territory. It was only with the adoption of the Thirteenth Amendment in 1865 that slavery was officially abolished in all of the United States.
Lincoln was still a hell of a president, one of the best in American history. But the mythology and reality of the American Civil War differ slightly.