What were the Southern states referred to during the Civil War?

During the Civil War, the Southern states formed a separate government known as the Confederate States of America. They seceded from the Union primarily over issues related to states' rights and slavery. The term "Confederates" specifically referred to those states that joined this new political entity, which fought against the Union forces. This label distinguishes the Southern states' stance and their collective identity during the conflict.

The other terms listed do not appropriately describe the Southern states during this period. The Union refers to the Northern states that remained loyal to the federal government. The Allies were nations involved in World War I and II, unrelated to the Civil War context. The Federalists were a political group in the early years of the United States, primarily associated with the support of a strong central government, which does not pertain to the Civil War era. Thus, "the Confederates" is the correct term to accurately identify the Southern states during the Civil War.