Union (American Civil War)
With northern states those states of the USA are referred to, further known to the United States, when / had split off in 1861 eleven southern states in 1860 and formed the Confederate States of America. Undecided or neutral states such as Maryland and Kentucky were set by both parties under pressure to join one side or the other. After the invasion of Confederate troops in Maryland that State concluded in the interest of self-defense of its own national laws to the Northern States, although it sympathized with the South in many ways - a secession from the Union did not come for Maryland but in question.
The northern states were in the legitimacy and in the continuity of previously existing political unit than through her to existing Union so that the Union also became synonymous term for the Northern States in their followers and the Confederate enemy.
The division into North and South has survived to this day and constitute a socio-cultural opposition that runs through all walks of life and polarized parties and any policy between the states and the federal government unspoken since the phase of Reconstruction. Only in the western U.S., who played a minor role in the American Civil War, this classification is not applicable.
The Mason - Dixon Line, named after the astronomer Charles Mason and surveyor Jeremiah Dixon, is in common usage, traditionally the boundary between the North and the South, although a state of the Northern states (Maryland ), and even the District of Columbia including the city of Washington south of this line are.