 Resentments about the treaties caused many members of the tribe to side with the British in the War of 1812.At the conclusion of the war, the tribes in the Treaties of Portage des Sioux reaffirmed the earlier treaties of 1815.In 1816, surveyor John C. Sullivan was instructed to survey the Osage territory starting 20 WEST of Fort Clark at the confluence of the Kansas River and Missouri River.