The Louisiana Purchase In 1803, the United States was just 20 years old. There were 17 states in the Union and the American territory reached only as far West as the Mississippi River. On the other side of the Mississippi between the river and the Rocky Mountains, was the unexplored Louisiana Territory. In 1800 Napoleon, emperor of France had taken Louisiana back from Spain who ruled it since 1763. President Jefferson did not want the French army threatening America's western …showed first 75 words of 1146 total…

…showed last 75 words of 1146 total…Trail that crossed the Rocky Mountains from the Great Plains. John McLaughlin, the British commander of Fort Vancouver, became a citizen of the United States.- The United States and Great Britain finally settled their differences over the region in 1846. By the Oregon Treaty, the two nations established the modern boundary of the United States and Canada. The states Washington, Idaho, Montana, North Dakota, and Minnesota all share this imaginary line as their northern border.