Simplify the following text for a Grade 11 native English-speaking person.
Original: Eleven Southern slave states declared their secession from the United States ( said that they wanted to separate from the United States of America ) and formed the Confederate States of America , also known as `` the Confederacy '' .
Simplified: Eleven Southern slave states declared their secession from the United States and formed the Confederate States of America , also known as `` the Confederacy '' .