Okay, it's about time I wrote this. Excuse me for not being too active lately, I've been extremely busy, and it's not going to stop any time soon.
So the American Civil War it is. The war lasted from 1861 to 1865, and claimed more than 600,000 lives.
What they say it's about:
A crusade against slavery, by the honourable, brave and fair president Lincoln.
What it's really about:
Pretty much everything that divides the South from the North.
The Southerners were mainly Catholics, while the Northerners were mainly Protestants.
The Southerners owned huge plantations where they farmed mainly tobacco, cotton or corn, using slave power, while the middle-class Northerners owned smaller farms where they used more modern technology. Please also note that slave plantations actually weren't as inefficient as most people think.
The Southerners needed to export goods like tobacco and cotton, and import necessities, while the North was self-sufficient, therefore the South advocated free trade, while the North advocated protectionism.
The Southerners voted mainly for the Democrats, who advocated a small federal government and a strong state, while the Northerners voted mainly for the Republicans, who advocated a strong federal government.
The slavery question was handled individually by each state, and Lincoln was not in favour of abolishing slavery, Lincoln was actually a moderate in the slavery question. On the other hand, Lincoln campaigned against the expansion of slavery to the new states in the West (acquired from Mexico after the Mexican-American War). The conflict started because naturally and geographically, states like California would have had close ties with the South, however the Railways from the North resulted in very close ties with the North instead.
Lincoln won the election in 1860, much to the dismay of the south, although he only got about 39% of the votes. Lincoln won in a similar way that George W. Bush won in 2000. To protect their interests, some Southern states seceded, creating the Confederate States of America (aka the Confederacy). In the constitution, there was no clear instructions as to whether or not states have the right to secede or not, and neither was there any instructions about what should be done if states do secede.
Hostilities started when South Carolina's (one of the states that seceded) authorities wanted to seize a fort occupied by the federal US Army. The Confederate forces had to bombard the fort until it surrendered, which Lincoln considered an attack on the USA. After the incident, Lincoln called for volunteer armies from all the states to take back federal property from the Southerners, starting the Civil War, and causing some more states to secede in the process. Remember: Slavery was still legal in some of the Northern states. Ending slavery was not the goal of the war, however, in the middle of the war, Great Britain threatened to intervene in favour of the South. To stop this, Lincoln made ending slavery in the South a war goal, as Great Britain didn't want to openly support slavery.
The American Civil War was thus not really about slavery, but mainly about the role of the federal government and the right of states to secede from the union. There, one more common historical misconception fixed.