The history of Missouri begins with settlement of the region by indigenous peoples during the Paleo-Indian period beginning in about 12,000 BC. Subsequent periods of native life emerged until the 17th century. New France set up small settlements, and in 1803 Napoleonic France sold the area to the U.S. as part of the Louisiana Purchase. Statehood for Missouri came following a compromise in 1820 that allowed slavery. Settlement was rapid after 1820, aided by a network of rivers navigable by steamboats, centered in the dominant city St. Louis. The Civil War saw numerous small battles and control by the Union. After the war, its economy became more diverse, and railroads, centered in Kansas City, opened up new farmlands in the west. In the early 20th century Progressive reforms sought to modernize state and local government and minimize political corruption. During the 20th century, Missouri's economy diversified further, and it developed a balanced agricultural and economic sector. By the 21st century manufacturing was fading, as service industries grew, especially in medicine, education and tourism. Agriculture remained profitable, as the farms grew larger and fewer people lived on them.