In the context of US history, 1820 refers to the year when an important legislation called the Missouri Compromise was passed. It was an attempt to maintain a balance of power between slave and free states in the United States.
Related terms
Missouri Compromise: This legislative agreement admitted Missouri as a slave state and Maine as a free state, while also establishing a line (36°30' parallel) across the Louisiana Territory, stating that all future states north of that line would be free while those south of it could allow slavery.
Slave States: Refers to states where slavery was legal and practiced before its abolition in the United States.
Free States: Refers to states where slavery was prohibited or abolished prior to or during the Civil War era.