A Brief History
In 1800, America's western border reached only as far as the Mississippi River. Following the Louisiana Purchase in 1803 the country nearly doubled in size and pushed its western edge past the Rocky Mountains. Yet the wilderness known as Oregon Country (which included present-day Oregon, Washington and part of Idaho) still belonged to the British, a fact that made many Americans eager to settle the region and claim it for the United States.
American Indians had traversed this country for many years, but for European Americans it was unknown territory. Lewis and Clark's secretly funded expedition in 1803 was part of a U.S. Government plan to open Oregon Country to settlement. However, the hazardous route blazed by this party was not feasible for families traveling by wagon. An easier trail was needed.