Fifteen years later, in 1819, President James Monroe dispatched a military expedition (the Yellowstone Expedition, led by Colonel Henry Atkinson) to establish a series of forts along the Missouri. These forts were to support the American fur trade and counteract British influence on the northern plains. The 6th US Infantry and 1st Rifle Regiments made up the military portion of the expedition, which arrived at the Council Bluff site on September 19. Their establishment of Fort Atkinson made it the first major American fort west of the Missouri River. It was located near Fort Lisa and Cabanne's Trading Post, private fur trading establishments operated by major traders who were based in St. Louis, Missouri.