 The fourth of these, in 1806, consisted of over 600 men under Lieutenant Facundo Melgares; its size was intended to impress the Native Americans of the area and to secure their cooperation with Spain against the United States.The United States also sent out an expedition in 1806.General James Wilkinson, the newly appointed governor of the Louisiana Territory, dispatched Zebulon Pike and 23 men to explore the headwaters of the Arkansas and Red Rivers, to negotiate peace between the Native American tribes of the area, and to contact the Comanche of the High Plains.