 The United States acquired the rest of Upper Louisiana in the Louisiana Purchase of 1803; military rule continued for a few months before it was transferred to civilian government, first under the Indiana Territory, and then as the Louisiana Territory in 1805.This period included the entire Mississippi River and Missouri River basin above the mouth of the Arkansas River.After the Seven Years' War ended in 1763, the Treaty of Paris awarded Great Britain the east bank of the Mississippi, from below Baton Rouge northwards.