In 1803, France offered to sell the Louisiana Territory to the United States for $15 million

 Although Jefferson, who had become the nation’s third President, was not sure if the Constitution allowed the federal government to buy territory, he went ahead with the purchase - he uses the Elastic Clause

The Louisiana Purchase doubled the size of the United States

The territory included all the area between the Mississippi River and the Rocky Mountains

Jefferson believed American control of the Mississippi River would provide an opportunity for farmers to move further west and have free transport of the sea

Thus, Americans gained full control of the Mississippi River, the port of New Orleans (connecting the Mississippi River to the Gulf of Mexico), and the Great Plains