After Mexico won independence from Spain in 1821, Americans were welcomed and encouraged to trade, and commerce quickly flourished, linking the economies of Missouri and Mexico. The Santa Fe Trade grew into a complex web of international business that brought together a cultural mosaic of individuals who cooperated and at times clashed, while the rich culture of the Plains Indian people was caught in the middle. Teamsters faced 781 miles of semi-arid prairies, storms, flooded rivers, wildfires, dust, plagues of gnats and mosquitoes, mud, and dangers from Comanches, Kiowas, Cheyennes, Arapahos, and Apaches, though freight wagons could make the one-way trip in eight weeks with luck. For 60 years the Santa Fe Trail was one of the most important overland trade routes in the world. The United States Army depended on freight shipments from the East to supply posts throughout the Southwest, and following the Mexican-American War from 1846 to 1848, most American freight was military while Mexican freighters bound east dominated the civilian trade. Fort Larned, 20 days' travel west of the Missouri River steamboat landings, helped guard the tens of millions of dollars in Santa Fe Trail traffic that crossed the Great Plains each year.