Final answer:
The United States gained the greatest amount of territory from France through the Louisiana Purchase, which doubled the size of the nation and expanded its territory westward.
Step-by-step explanation:
After the Louisiana Purchase, the United States gained the greatest amount of territory from France. This historic agreement, negotiated by President Thomas Jefferson's envoys, Robert Livingston and James Monroe, was signed in Paris on April 30, 1803. Jefferson sought to secure American commerce through the port of New Orleans and ensure access to the Mississippi River. Despite concerns about constitutional authority, Jefferson proceeded with the purchase, motivated by the vision of an agrarian republic and the opportunity presented by Napoleon's willingness to sell. The deal was finalized for $15 million, effectively doubling the size of the nation and expanding it westward beyond the Mississippi River, up to the Canadian border. The acquisition laid the groundwork for further westward expansion and significantly shaped the future development of the United States.