who claimed oregon county
Landscape in Oregon Country (Charles Marion Russell) The territory became a focus of those who believed that it was the United Statesâ obligation and right to extend its rule and liberties across the North American continent. The Oregon Territory stretched from the Pacific coast to the Rocky Mountains, encompassing the area including present-day Oregon, Washington, and most of British Columbia. Originally Spain, Great Britain, Russia, and the United States claimed the territory. In 1819, under terms of the Transcontinental Treaty, Spain ceded its claims to the territory to the United States.