My favorite books on Abraham Lincoln and the Civil War are still boxed up from the move, but this is my best recollection of the relevant material. The founding fathers of this country were deeply aware of the moral problem of allowing slavery and they knew that it would have to be confronted at some point. In order to have a chance of successfully breaking away from England, the issue was put on hold. After the invention of the cotton gin changed the economics of processing raw cotton and thereby the price of cotton finished goods, the practice of growing cotton with slave labor spread widely throughout the South. Even as this was happening during the early 1800's, the Quakers were growing quite vocal about the abolition of slavery. Eventually other groups picked up the banner of abolition. Many but not all of these groups were deeply religious and various sects of the church split on opposite sides of the issue. Political deals like the Missouri Compromise continued to punt the issue.
As Bret mentioned, the government instituted and enforced laws which preserved slavery. Abolition was a hot issue of the day, but it was not the major issue behind the civil war. This country was founded as part of a tax revolt and that was the major issue behind the Civil War. The industrial North wanted the mercantilst protection of high tariffs and customs while the agrarian South wanted low trade barriers(the South paid the bills under a high tariff regime). The South said 'no mas' and threatened to secede. Lincoln decided to fight in order to preserve the existing order. It is no accident that the fighting began at Fort Sumter, a customs house. Yes, there were other issues, but they were of lesser importance. Lincoln was a very skillful politician and he timed the signing of the Emancipation Proclamation to sway public opinion and demoralize the South. It freed slaves only in the states of rebellion not already under Union control. If Lincoln did not feel it was politically advantageous then abolition would have had to wait. There are also arguements that the economics of slavery were in decline and that the practice was doomed. I have not done enough study to know how valid this view might be.
This is not how these events are portrayed in junior high school history class, but I think this is quite valid. Now, how much credit do you want to give government for ending slavery?