Sarah A Koos was 11 years old when American Civil War: Fort Sumter surrenders to Confederate forces. The American Civil War was a war fought in the United States from 1861 to 1865. As a result of the long-standing controversy over slavery, war broke out in April 1861, when Confederate forces attacked Fort Sumter in South Carolina, shortly after U.S. President Abraham Lincoln was inaugurated. The nationalists of the Union proclaimed loyalty to the U.S. Constitution. They faced secessionists of the Confederate States, who advocated for states' rights to expand slavery.