Thanks for your question! The excellent answers above made me wonder if slavery might have persisted, in some ways and to some degree, even after the end of the Civil War. Apparently it did to a very minor extent. The Wikipedia article on slavery has some interesting paragraphs on this topic, and I also found the following link, which provides some fascinating documentation of the persistence of slavery after the end of the war:
The Constitution almost completely ignores the issue of slavery before the Civil War. Even the 1808 import ban was only agreed upon because the slave population of North America was self sustaining by that point.
So the only way the issue was "settled" (and one can argue that such an issue couldn't be settled by force of arms) was through the Union victory in the Civil War and the 13th Amendment. Even then, the lives of southern blacks was largely unchanged from the days of slavery.
Because of the way your question is worded, I'm wondering if you're asking about how it was settled in the Constitution. Slavery was never actually mentioned, but it was clearly allowed. The Constitution said the following about slavery:
- 3/5 of slaves would be counted when trying to determine how many Representatives each state got in the House.
- Fugitive slaves had to be returned to the states from which they escaped.
- The slave trade could not be abolished until 1808.
In this way, slavery was accomodated in the Constitution but not as much as Southerners would have liked.
The above post provides some excellent answers to your question. Inevitably, it was the Civil War and Lincoln's Emancipation Proclamation that effectively ended the slavery debate. The importation of African slaves had been made illegal long before the Civil War, and even if the war had not occurred, worldwide public opinion would have eventually put an end to America's dependance on slavery, since most of the civilized world had abolished it by the 1880s.
Slavery had existed in all states at some point prior to the war; however it died a natural death in the northern states because the north was not dependent on a labor intensive agricultural economy as was the South. The foreign slave trade was ended by the Constitution itself which specified a date of 1808 when it could be ended (it actually states it could NOT be ended before that date.) In point of fact, Congress outlawed the trade on January 1, 1808, the earliest date constitutionally possible.
Slavery was actually ended by the 13th Amendment to the Constitution, passed at a time when Southern states were not represented in Congress. Many were required to ratify the amendment as a condition of seating delegates to Congress at the end of the Civil War, so the above answer is somewhat correct. It is a bit simplistic, however, to state that the war was fought solely over slavery. There were larger issues to be decided; however slavery was the catalyst that ignited the flames of war.
Long answer short, the Civil War. In the Civil War, the main thing that the North and the South were fighting about was the issue of slavery. It was through the North's victory that the issue of slavery was, for lack of a better word, determined.