The French sold the Americans 828,000 square miles of land west of the Mississippi River in a treaty called the Louisiana Purchase. The treaty was signed on April 30, 1803. The Americans wanted Louisiana because of the Port of New Orleans. This was the most widely used port, because it was at the bottom of the Mississippi River, and that river was their main way of trading goods with other states. Americans got tired of relying on the French, and bought Louisiana and other present day states.