After the Revolutionary War, Americans began to settle in the Ohio River valley. The Appalachian Mountains made it very expensive and difficult to transport goods to the east coast. The cheapest way to ship goods to the coast was to float them down the Ohio River, then down the Mississippi River to New Orleans, where they could be transferred to ocean going vessels for shipment to the east coast and Europe. The problem was that the U.S. had no control over New Orleans and Thomas Jefferson, president at the time of the Louisiana Purchase, feared that the U.S. would lose its right of deposit at New Orleans. At the time, Louisiana was controlled by Spain, but in a secret agreement, Spain was to cede Louisiana to France in exchange for a Spanish Kingdom in Italy. With knowledge of this agreement, Jefferson sent Robert Livingston, and then James Monroe, to France to negotiate the purchase of New Orleans from Napoleon for $10 million. With the hopes of a Caribbean empire based on the sugar trade dashed with the loss of Santo Domingo, Napoleon lost interest in controlling Louisiana. In need of money to continue his European wars, Napoleon offered the U.S. the entire Louisiana territory, more than 800,000 square miles, for $15 million. One problem confronted Jefferson. He was a strict constructionist and did not see anything in the Constitution which would give him the power to purchase Louisiana. What he did know was that he did have the power to negotiate treaties. Knowing that this deal was in the best interest of the United States, he put the purchase of Louisiana in a treaty which the Senate later ratified. In 1830, the United States doubled in size with the purchase of Louisiana from Napoleon for $15 million.
I need to correct my last post. The last line of my post should read, "In 1803, the United States doubled in size with the purchase of Louisiana from Napoleon for $15 million."
Jefferson was interested in buying the Louisiana Purchase because he wanted to make the United States bigger, well-fit, and stronger. He also was interested in the buying the land because he was fearful that foreign countries would control the New Orleands port.