Final answer:
Jefferson agreed to the Louisiana Purchase to fulfill his vision of an agrarian society, the importance of control over New Orleans and the Mississippi, and due to the opportunity presented by France's willingness to sell the territory at a bargain price, despite constitutional concerns.
Step-by-step explanation:
Thomas Jefferson agreed to the Louisiana Purchase despite his doubts about its constitutionality because the opportunity aligned with his vision for the United States. Jefferson's belief in the importance of land for an agrarian society, along with the value of controlling New Orleans and the Mississippi River for trade and expansion, outweighed his constitutional concerns. The acquisition of the Louisiana Territory from France at the cost of $15 million not only doubled the size of the nation but also provided farmable land crucial for Jefferson's desired expansion of yeoman farming. This was a significant move to bolster the agrarian republic and ensured control over pivotal trade routes.
The decision to proceed with the purchase also came against the backdrop of shifting international dynamics, particularly with France's loss of interest in maintaining its American territories after the Haitian Revolution. Despite the fact that the Constitution did not explicitly grant the President the power to acquire new land, the benefits deemed in acquiring the vast territory for a bargain price prevailed, particularly with Napoleon's willingness to sell. Thus, Jefferson assigned Robert Livingston and James Monroe to complete the transaction, making one of the most notable real estate deals in American history, which significantly expanded the United States and fueled Jeffersonian democracy.