The natural feature that separates the United States from Canada is the border, which is the longest international land border in the world. Stretching over 5,525 miles, this boundary has intricate markings that run through forests, rivers, mountains, and plains. Key landmarks include the Great Lakes, which are shared by both countries, and various border crossings that facilitate trade and travel between the two nations. The border is also characterized by historical treaties and agreements, showcasing rich diplomatic relations. Additionally, it features the famed 49th parallel, which is a significant line of latitude marking much of the U.S.-Canada border.