Original sentence: Seven states declared their independence from the United States before Abraham Lincoln was inaugurated as president; six more did so after the American Civil War began with the Battle of Fort Sumter when the CSA attacked the USA
Edited sentence: Seven states declared their independence from the United States before Abraham Lincoln was inaugurated as president; six more did so after the American Civil War began with the Battle of Fort Sumter when the CSA attacked Fort Sumter, South Carolina, which was ocupied by the USA