In 1803, which territory did France sell to the United States, stretching from the Mississippi River to the Rocky Mountains?

The Louisiana Purchase is the correct answer because it refers to the acquisition of a vast territory by the United States from France in 1803. This land extended from the Mississippi River to the Rocky Mountains, effectively doubling the size of the United States at the time. The purchase was significant not just for its size, but also for its implications for westward expansion, exploration, and settlement.

By acquiring this territory, the U.S. gained control over key trade routes and resources, and it laid the foundation for the country's future growth. The sale was motivated by France's need for funds for its military campaigns in Europe as well as its challenges in governing vast territories in North America. This momentous deal was negotiated by President Thomas Jefferson, who sought to secure land for future generations.

The other options refer to different territories or purchases. Florida Territory was acquired later from Spain; Texas Territory was an independent republic before becoming a state; the Oregon Territory was settled through treaties and expansion efforts rather than a single purchase. Understanding these distinctions is important for grasping the broader scope of U.S. territorial expansion.