For 60 years the Santa Fe Trail linked the Eastern states and the Southwest, as hundreds of freight wagons laden with trade items traveled the 900 miles between Mexico, present-day New Mexico, and Missouri in six to ten weeks at 18 to 21 miles a day. Crossing lands used by U.S. citizens, Mexicans, and Plains Indians, the trail fostered both cooperation and conflict. The Arkansas River to the south was once an international boundary between Spain and the United States, and after Mexico gained independence in 1821, Mexicans and Americans developed a lively and profitable trade along the route. Cloth, hardware, notions, and even canaries went west from Missouri and Kansas to New Mexico, while wool, silver coins, Mexican jacks, and jennets were hauled to the United States. In 1846, U.S. troops used the trail to invade and seize Mexico and the Southwest during the Mexican-American War, and when the war ended two years later the boundary shifted closer to its present-day location, turning the route from an international freight road into a national road. Military freighting then increased as army posts were established to protect travelers, but by the 1860s the railroad was pushing westward and replacing the trail until it reached Santa Fe in 1880.