The Louisiana Purchase was the acquisition of the territory of Louisiana by the United States from Napoleonic France in 1803 for a price of $15 million. The Louisiana territory stretched from the Mississippi River in the east to the Rocky Mountains in the west and from the Gulf of Mexico in the south to the Canadian border in the north. These were the most important achievements of Thomas Jefferson’s presidency. 

When France explored the Mississippi River Valley at the beginning of the 17th century, they established scattered settlements in the region. During the middle of the 18th century, France controlled more of the United States than any other European power. In the French and Indian War of 1762, the French ceded the French Louisiana West of the Mississippi River to Spain, transferring all of its extra remaining North American holdings to Great Britain in 1763. In 1796, Spain had allied itself with France, which led Britain to use its powerful navy to cut Spain off from America. In 1801, a secret treaty was signed by Spain and France to return the Louisiana Territory to them. When France was taking control of Louisiana, it was very slow. In 1802, the Spanish authorities acted under French orders that revoked a US-Spanish treaty that ended up granting Americans the right to store goods in New Orleans. Jefferson responded by sending future president James Monroe to Paris to aid Livingston in the New Orleans purchase talks. The French asked a surprised Livingston if the United States was interested in purchasing all of the Louisiana Territory.

The treaty was dated April 30th and signed on May 2nd. In October 1803, the United States Senate ratified the purchase, and France delegated authority over the region to the United States. Jefferson commissioned the Lewis and Clark expedition to explore the territory acquired by the Louisiana Purchase. Exactly nine years after the Louisiana Purchase agreement was made, the first state that was carved from the territory of the Louisiana Purchase was admitted into the Union as the 18th US state.