The Eastern United States or the American East, is today defined by some as the states east of the Mississippi River, and is traditionally divided by the Ohio River and Appalachian Mountains into the South, the Old Northwest and the Northeast. The first two tiers of states west of the Mississippi have traditionally been considered part of the West, but can be amalgamated with states of the Old Northwest into what the Census Bureau defines as the Midwestern United States. It has been considered part of the Eastern United States in regional models that exclude a Central region.