Constance Sharp 
Thomas Jefferson and the Growing United States (1800-1811) 

The United States’ boundaries have expanded over the centuriesand at the same time, Americans’ ideas about their country have grown as well. The nation the world knows today was shaped by centuries of thinkers and events. Thomas Jefferson was one of the most important of these thinkers. During his presidency, the Louisiana Purchase doubled the geographic size of the United States. And perhaps most important, Jefferson helped define what is best about America.