1. In the 19th century, industry bloomed in the (rich) Northern states. Railroads and factories popped up everywhere. The main industry in the Southern states however still lay in (cotton) farming. Whereas the North had already realized that slaveholding is immoral and had abolished slavery in the late 18th century, the Southern economy was still heavily dependent of slaves.
2. Anti-slavery Abraham Lincoln was elected president of the United States in 1860 without carrying a single Southern state. The Southern states felt they were losing representation in the Union, and that in turn would mean they would lose power in the slavery question and other policies. Because their economy would fall apart when slavery would be forbidden, the only option left for them seemed to leave the Union.
3. South Carolina was the first state to secede in December 1860. Six more states (dark red) seceded in January/February 1861. Four more states left the Union a few months later (light red) and called themselves the Confederate States of America. To their opinion, they were sovereign states within the Union and thus had the right to leave whenever they liked, whereas the Northern states found the Union was only possible if all member states were and stayed united. The North therefore didn't recognize the secession as legal.
4. Jefferson Davis, the US senator in Mississippi with a strong military past, was elected President of the Confederate States in February 1861. He was chosen because of his strong political and military credentials.
5. The 'real' war started when Fort Sumter was attacked by Confederates claiming the fort belonged to them. Initially the North states just wanted to restore the Union, but then wanted to destroy the Confederate States and the institution of slavery with them. The Conferderate army was heavily outnumbered (21 million people were living in the North in contrast to 9 million in the South), but that didn't scare them off initially. It wasn't so long ago since the outnumbered Americans had won a war against the way more mighty Britain.
6. A couple of slave states (Delaware, Kentucky, Maryland, and Missouri) didn't leave the Union. Keeping control of the border states played an important role in the victory for the Union, since they meant an advantage in troops, factories and money. However, not everyone in the border states supported the Union: Many soldiers headed south and joined the Confederate Army.
7. In 1861 and 1862, many battles were fought with heavy losses on both sides. Some of the major battles included the First Battle of Bull Run (July '61, won by the Confederacy), the Battles of Shiloh (April '62) and of Antietam (September '62, both won by the Union) and the battle of Fredericksburg (December '62, won by the Confederacy).
8. On January 1, 1863, President Lincoln proclaimed that all slaves in the Confederate states were free. (Note: as a consequence, slavery still legal in the border states!). The freedom wasn't giving immediately however, and most slaves had to wait until the end of the war. Around 200,000 blacks joined the Union Army to fight against the Confederates and helped their brothers to freedom.
9. During Battle of Gettysburg of July 1-3, 1863, over 23,000 soldiers were lost on each side, but the Union army of the Potomac defeated the attacks by Confederate General Robert E. Lee's army of Northern Virginia. His defeat ended Lee's attempt to invade the North, which is why this battle is seen as the turning point of the Civil War.
10. On April 9, 1865, General Robert E. Lee surrendered. Other generals of Confederate armies followed within the next weeks. Jefferson Davis was captured in May and spent the next two years in prison.
For Lincoln, peace didn't last long. Five days after the surrender of General Lee, he was assassinated while attending a play at Ford's Theatre in Washington D.C. The assassination was planned and carried out by stage actor John Wilkes Booth, as part of a larger conspiracy in a bid to revive the Confederate cause. The plan didn't work out however: the Confederacy was dissolved in May 1865 and and the American States where reunited. All remaining slaves were set free in December.
Unfortunately, the freeing of blacks didn't change anything to racism. In the Southern states for instance, people began to refuse black attending schools.