It is easy to date the “official” American Civil War. It occurred between 1861 and 1865. It is far more complex to answer the question whether the Battle of Appomattox truly resolved what so deeply divided the United States of America back then.
At the crux of the matter was the so-called 3/5ths Compromise at the U.S. Constitutional Convention of 1787. The position of the states in the country’s South, where most slaves lived, was that slaves should count as much as “free men” but only when determining the number of each state’s seats in the U.S. House of Representatives.
According to the South, slaves should not be accounted for at all when it came to establishing every state’s tax obligations towards the federal government. These were determined at the time by the size of a state’s population. The South viewed slaves solely as the property of their owners. The North took the opposite view.
The outcome of this dispute was an agreement that slaves should be accounted for as 3/5 of a free person for both purposes — representation and taxation. As the years went by, and as the nation grew from 13 founding states to 34 states in 1860, this unholy compromise caused deep political imbalances.
As a result of that expansion, the South had a near-stranglehold on the House of Representatives and the presidency (with all its military and foreign policy powers) through the Electoral College.