Why is the louisiana purchase treaty an important document in the study of manifest destiny?

The Louisiana Purchase treaty is an important document in the study of Manifest Destiny because it represents the largest territorial expansion in the history of the United States, framed within Manifest Destiny's ideology of the 1800s.

Explanation:

The Louisiana Purchase was the US acquisition from the French in 1803 of 2,140,000 km² of territory then known as the French Louisiana. The cost was $ 11,250,000, which added to the extinction of debts and interest reached the total amount of $23,213,568.

With this acquisition of territory the United States doubled its surface and its dominion was extended over the entire Mississippi-Missouri basin, reaching the border of the Rocky Mountains, expanding West just as the Manifest Destiny encouraged to do.