Final Answer: The slave states that remained in the Union as other Southern states seceded were Delaware, Maryland, Kentucky, and Missouri.
Explanation:
During the American Civil War, while many Southern states seceded from the Union to form the Confederate States of America, a few slave states chose to remain within the Union. These states included Delaware, Maryland, Kentucky, and Missouri. Although these states permitted slavery, they did not secede from the Union. Their decision to stay was influenced by various factors such as strategic considerations, economic ties, internal divisions, and political leadership. Despite being slave states, they maintained their allegiance to the United States throughout the Civil War. This distinction is significant in understanding the dynamics of the conflict and the diverse positions taken by states regarding the issue of slavery and secession. Therefore, these four states are recognized for their unique position during this turbulent period in American history.