Lewis and Clark's greatest accomplishments were their scientific expeditions, which greatly added to the knowledge of the American continent. Their expedition lasted from 1804 to 1806 and covered over 8,000 miles. They mapped new territory, recorded weather conditions, animal life, and plant species, and established trade relations with Native American tribes. They also provided valuable information about the geography and resources of the Louisiana Territory, which was acquired by the United States in 1803. The expedition also helped to strengthen American claims to the Oregon Country, which was later disputed by Great Britain.