Final answer:
The land deal that doubled the size of the United States on October 20th, 1803, is known as the Louisiana Purchase, where the U.S. acquired territory from France for $15 million under Thomas Jefferson's presidency.
Step-by-step explanation:
The Louisiana Purchase
The land deal that doubled the size of the United States on October 20th, 1803, was known as the Louisiana Purchase. President Thomas Jefferson, driven by his vision of an "empire of liberty," orchestrated the acquisition to expand the nation and promote his agrarian republican ideals.
The United States bought the vast Louisiana territory from France for $15 million, a significant bargain considering the sheer magnitude of land involved. While initially interested in New Orleans for its strategic importance to trade and navigation along the Mississippi River, the opportunity to purchase the entire territory was too good for Jefferson to pass up, despite his strict adherence to the Constitution that did not expressly grant him such power.
The Louisiana Purchase greatly impacted American history, not just geographically, but also economically and culturally. It opened the American West to exploration and settlement, leading to the creation of new states and raising questions about the extension of slavery into the new territories.