Soon after Thomas Jefferson became President, the United States learned that Spain planned to return Louisiana to France. Fearing that France might try to interfere with Western American trade in the port of New Orleans, Jefferson instructed special envoy James Monroe and American Minister to France Robert Livingston to discuss with the French the possible to purchase of the port of New Orleans. Monroe and Livingston were astonished when Francois Barbé-Marbois, at Bonaparte's order, offered the entire Louisiana Territory to the United States. Although they lacked Constitutional authority, the American representatives agreed to buy all of the massive territory which extended from Canada to the Gulf of Mexico and from the Mississippi River to the Rocky Mountains for a total of nearly fifteen million dollars -- an extraordinary bargain at four cents an acre. A Treaty of Cession was signed on April 30, 1803 in Paris. President Jefferson, a believer in strict adherence to the Constitution, was concerned about the legality of purchasing Louisiana before the agreement could be ratified by the Senate but he supported the decision made by Monroe and Livingston. Debate over the purchase and over the addition of an "alien population" to the United States was intense with the New England states eager to condemn the acquisition of Louisiana and the frontier states of the South and West just as eager to defend it. On October 25, the Treaty of Cession was approved by the Senate and, shortly thereafter, the transfer of power took place in New Orleans. By the single act of purchasing the Louisiana Territory, the United States of America doubled its size and greatly accelerated its march toward the Pacific coast. The beckoning West awaited a new generation of pioneers who would turn the dream of "manifest destiny" into the reality.