Between 1801 and 1861, the United States underwent vast westward expansion and settlement as exploration was encouraged. The Louisiana Purchase doubled the size of the country, and territories like Florida, Texas, Oregon, and California were added through treaties and war. Westward migration was influenced by geographic and economic factors like availability of land, economic opportunities from gold rushes or farming, and new transportation technologies. African Americans, Chinese immigrants, and Native Americans all contributed to westward expansion.