Jeffersonian Democracy and Territorial Expansion

During the presidency of Thomas Jefferson, a key aspect of his administration was the belief in a democratic approach to governance, which is commonly referred to as Jeffersonian Democracy. Jefferson advocated for an agrarian society, civil liberties, and a limited federal government. One significant event during this period that exemplified Jefferson's approach was the purchase of a large territory from France in 1803. This acquisition had lasting implications for the United States in terms of expansion and governance.

What was this major territorial acquisition called?