Union: The Union refers to the Northern states that remained loyal to the United States during the Civil War.
Secession: Secession is the act of formally withdrawing from an alliance or organization. In this case, it refers to the Southern states withdrawing from the United States.
Emancipation Proclamation: The Emancipation Proclamation was an executive order issued by President Abraham Lincoln in 1862, which declared that all slaves in Confederate territory were to be set free.