What 1803 agreement more than doubled the land area of the United States?

The Louisiana Purchase was the 1803 agreement that more than doubled the land area of the United States.

The United States acquired approximately 828,000 square miles of territory from France for $15 million. The land stretched from the Mississippi River to the Rocky Mountains and from the Gulf of Mexico toward the Canadian border. President Thomas Jefferson authorized the purchase, which was negotiated by James Monroe and Robert R. Livingston.

The agreement gave the United States control of the port of New Orleans and the Mississippi River, vital routes for trade and settlement. It also opened a vast region to American exploration, including the Lewis and Clark expedition, which began in 1804.

The purchase created constitutional uncertainty because the Constitution did not clearly state that a president could acquire foreign territory. Jefferson nevertheless supported the treaty, and the Senate ratified it in October 1803.