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The Louisiana Purchase in 1803 was a momentous event for the United States, doubling its size overnight with the acquisition of the vast Louisiana Territory from France for $15 million. This territory stretched from the Mississippi River to the Rocky Mountains, providing crucial access to the port of New Orleans and opening up expansive lands for settlement and exploration. The purchase facilitated westward expansion, including the famous Lewis and Clark Expedition, and solidified America's position as a continental power. It also sparked debates about presidential authority and constitutional interpretation, but ultimately shaped the nation's growth, identity, and manifest destiny across North America.