In the early 19th century, the United States experienced economic, social, and political instability. However, the Louisiana Purchase in 1803 doubled the country's size. After defeating Britain in the War of 1812, the U.S. emerged as an established world power. Americans then embarked on a period of dramatic growth, including westward expansion, population growth, industrialization, and the rise of cities. Cultural figures like Emerson and Thoreau helped develop a uniquely American identity during this transformative era.