Final answer:
The Louisiana Purchase Treaty was signed on April 30, 1803, by Robert Livingston and James Monroe, doubling the size of the U.S. for $15 million.
Step-by-step explanation:
The LA Purchase treaty was signed in Paris by American envoys Robert Livingston and James Monroe on April 30, 1803. This historic deal, negotiated with France, resulted in the United States acquiring the Louisiana Territory, which effectively doubled the size of the nation.
President Thomas Jefferson, despite his reservations about Constitutional authority, saw the necessity for the acquisition to realize his vision of an expansive agrarian society. The transaction was a remarkable deal at the cost of $15 million, considered a bargain price, ensuring American access and control of New Orleans and the Mississippi River, significant for trade and expansion.