The Ohio River is the largest tributary, by volume, of the Mississippi River. It is approximately 1,310 miles (2,108 km) long and is located in the Eastern United States. Today, it forms the border between the western border of West Virginia and Ohio.
The river had great significance in the history of the Native Americans, as numerous civilizations formed along its valley. In the five centuries prior to European contact, the Mississippian culture built numerous regional chiefdoms and major earthwork mounds in the Ohio Valley, such as Angel Mounds near Evansville, Indiana, as well as the Mississippi Valley and the Southeast. For thousands of years, Native Americans, like the European explorers and settlers who followed them, used the river as a major transportation and trading route. Historically the Ohio Valley was territory of the Osage, Omaha, Ponca and Kaw, but they migrated west of the Mississippi River under pressure from Iroquois warriors. By the mid-17th century, they had settled in their historic grounds in Missouri, Arkansas, and Oklahoma and nearby states.
Rene-Robert Cavelier, Sieur de La Salle led an expedition to the Ohio River in 1669; his French party were the first Europeans to see the river. After European-American settlement, the river served at times as a border between present-day Kentucky and Indian Territories. It was a primary transportation route for pioneers during the westward expansion of the early U.S. The Ohio flows through or along the border of six states, and its drainage basin encompasses 14 states. Through its largest tributary, the Tennessee River, the basin includes many of the states of the southeastern U.S.
During the 19th century, the river was the southern boundary of the Northwest Territory, and it served as the border between free and slave territory. It is sometimes referred to as the "Mason-Dixon line". It is commonly acknowledged as the western natural extension of the original Mason-Dixon line that divided Pennsylvania and Delaware from Maryland and West Virginia (then a part of Virginia). It was thus the unofficial and, at times disputed, border between the Northern United States and the American South or Upper South.
The Ohio River is a climatic transition area, as its water runs along the periphery of the humid subtropical and humid continental climate areas. It is inhabited by fauna and flora of both climates. In his Notes on the State of Virginia published in 1781-1782, Thomas Jefferson stated: "The Ohio is the most beautiful river on earth. Its current gentle, waters clear, and bosom smooth and unbroken by rocks and rapids, a single instance only excepted."11 - Wikipedia contributors. "Ohio River." Wikipedia, The Free Encyclopedia. 12 Jul. 2010. Web. 17 Jul. 2010.