Thomas Jefferson played a crucial role in the spread of democracy in the United States. As the primary author of the Declaration of Independence in 1776, Jefferson articulated the ideals of liberty, equality, and the pursuit of happiness, which became foundational to American democracy. His commitment to Enlightenment principles and belief in the importance of an educated citizenry influenced the development of democratic governance in the United States. Jefferson's presidency further advanced democratic ideals through the Louisiana Purchase and the Lewis and Clark expedition, expanding the nation and promoting the idea of a government accountable to its people.