A reference to the North in the United States typically means the states that fought against the Confederacy during the Civil War. The North includes Massachusetts, Connecticut, Maine, New Hampshire, Vermont, Rhode Island, Illinois, Indiana, Iowa, Kansas, Missouri, Nebraska, Minnesota, Michigan, Ohio, North Dakota, South Dakota, Wisconsin, New Jersey, New York and Pennsylvania.
The northern states are divided into four distinct regions, including New England, the Old Northwest, the Mid-Atlantic States and the Great Plains. At the time of the Civil War, South Dakota, Nebraska and North Dakota were not yet states, and while Missouri was a state, it was a slave state with different boundaries.
The Mason-Dixon Line is a well-known boundary that separates the North from the South. This line runs horizontally along the eastern portion of the United States, separating Pennsylvania from Maryland. Maryland is below the Mason-Dixon Line in the South, while Pennsylvania is above the line in the North. The Ohio River also served as a boundary between North and South during the Civil War era. At the time of the Civil War, there were 19 free states and 15 slave states. One catalyst of the Civil War was the extension of slavery into the Western territories.