His relationship with the Osage Nation became particularly important when, in 1787, the Spanish governor Esteban Miro ordered an end to trade with the Osage and began to prepare for war against them as a result of fighting between Osage and European settlers. Although the government continued its ban on trade with the Osage, Chouteau was able to defuse a conflict between Osage and Spanish-armed settlers through his intervention with Miro. In spite of continuing problems between the Osage and the Spanish government, Chouteau maintained good relations with the tribe. Although the trade ban was lifted in 1791, problems continued among Mississippi tribes and the settlers, including horse theft and threatened attack on an Osage delegation in St. Louis by rival tribes of Sac, Fox, Kickapoo, Mascouten and Winnebago warriors. In 1793, these problems culminated in an order from the Spanish Governor General Francisco Luis Héctor de Carondelet, in which all trade between settlers and tribes was to cease. Hector also ordered a military expedition against the Osage and other tribes. However, Hector was persuaded toward peace by an Osage delegation led by Chouteau to New Orleans in the spring of 1794. To convince Hector of peace, Chouteau promised a military fort built among the Osage at his own expense. In return, Chouteau was given a six-year monopoly on trade along the Osage River. After its construction in 1795, Fort Carondelet, although acting as a military base, was in practice a trading post for the Chouteau family. The fort also served as home to Chouteau's nephews, who gained valuable experience as traders. Through contacts at this post, Chouteau also negotiated construction of a second trading post among the Osage, located on the Verdigris River in eastern Kansas from 1795 to 1797. However, in 1799, new Spanish Governor General Manuel María de Salcedo began favoring a Spanish businessman instead of the Chouteau fur operation. Fort Carondelet was sold to the Spanish firm, but Chouteau continued trade with the Osage on the Verdigris. Yet the Spanish competition was short-lived, as the Louisiana Territory was transferred first to France in 1800, then the United States in 1803. Late that year, Chouteau provided valuable information to the Lewis and Clark Expedition about the population of the Louisiana territory, along with observations of wildlife and local villages. In early 1804, Lewis and Clark purchased materials from Chouteau's trading house in St. Louis, and on March