Left the Union is a term used to describe the secession of 11 Southern states from the United States in 1861. This event, known as the American Civil War, was the result of a long-standing disagreement between the North and South over the issue of slavery. The seven-letter crossword solution for this term is SECEDED, which means to withdraw formally from an organization or alliance. This is what the 11 Southern states did when they left the Union and formed the Confederate States of America.