Final answer:
The 11 southern states withdrew from the United States due to their support for slavery. They called themselves the Confederate States of America.
Step-by-step explanation:
The 11 southern states withdrew from the United States primarily because of their support for slavery. These states believed that the federal government's interference with their right to own slaves infringed on their states' rights. They saw secession as a way to protect their way of life and preserve their economic and social systems.
The 11 states that withdrew from the United States called themselves the Confederate States of America. This new nation was formed in 1861 and lasted until the end of the American Civil War in 1865.