The Trans-Appalachian West is the region between the Appalachian Mountains and the Mississippi River in North America. It stretches from the Canadian border south to Mexico.
In American history, the Appalachian Mountains were a major obstacle to westward expansion. Numerous Native American groups inhabited the area. The difficulty of moving people and goods across the mountain range and the fact that all waterways to the west of the mountains fed into the Gulf of Mexico, not the Atlantic, hindered the establishment of frontier settlements. The United States gained control of the Trans-Appalachian region after the Treaty of Paris in 1783, which ended the American Revolution. Treaties with the local Native American groups allowed a flood of settlement over the next 70 years. Nine states were formed out of the region.