[177] He unknowingly acquired the most fertile tract of land of its size on Earth, making the new country self-sufficient in food and other resources. The sale also significantly curtailed the European presence in North America, removing obstacles to U.S. westward expansion.[198]
Most thought that this was an exceptional opportunity, despite Republican reservations about the Constitutional authority of the federal government to acquire land.[199] Jefferson initially thought that a Constitutional amendment was necessary to purchase and govern the new territory; but he later changed his mind, fearing that this would give cause to oppose the purchase, and he, therefore, urged a speedy debate and ratification.[200] On October 20, 1803, the Senate ratified the purchase treaty by a vote of 24–7.[201] Jefferson personally was humble about acquiring the Louisiana Territory, but he resented complainers who called the vast domain a "howling wilderness".[202]
After the purchase, Jefferson preserved the region's Spanish legal code and instituted a gradual approach to integrating settlers into American democracy. He believed that a period of the federal rule would be necessary while Louisianians adjusted to their new nation.