Final answer:
The correct answer is B) Territorial Expansion, as America experienced a significant increase in its territory with the 1803 Louisiana Purchase, which more than doubled the country's size and set the stage for westward growth.
Step-by-step explanation:
At the time Jefferson made the Louisiana Purchase, America was undergoing territorial expansion. The purchase in 1803 more than doubled the size of the United States and paved the way for westward expansion, impacting Native American tribes, and raising questions about the extension of slavery into the new territories. It represented one of the greatest real estate deals in history and significantly changed the nation's trajectory, promoting Jefferson's vision of an agrarian republic and securing vital access to New Orleans and the Mississippi River for trade. Despite debates over the constitutionality of the purchase, it was widely celebrated and helped to cement Jefferson's reelection in 1804.