After crossing the Rocky Mountains, the expedition reached the Oregon Country (which was disputed land beyond the Louisiana Purchase) and the Pacific Ocean in November 1805. They returned in 1806, bringing with them an immense amount of information about the region as well as numerous plant and animal specimens. They demonstrated the possibility of overland travel to the Pacific Coast. The success of their journey helped to strengthen the American concept of "manifest destiny" – the idea that the United States was destined to reach all the way across North America from Atlantic to Pacific.