The American Civil War split the United States of America to northern and southern states and left a legacy of bitterness. Slavery was the prime reason here, as it was prevalent in many southern states.
In 1861, when Abraham Lincoln was elected as the president of US, he pledged to abolish slavery, and after this eleven southern states announced that they were breaking away from US. When the government told them that they could not do this, civil war broke out.
The actual war began when the United troops attacked the Union garrison in South Carolina. The Confederate Army fought for the Southern states and the Union Armies for the government. A lot of credit is given to Ulysses S. Grant who led the Union Armies to victory; he went on to become the president of US in 1869.
In 1865, Union Armies captured the states, but it was also the year when Abraham Lincoln was going to assassinated.