Native Americans in the United States resided in what is now Iowa for thousands of years. The written history of Iowa begins with the proto-historic accounts of Native Americans by explorers such as Marquette and Joliet in the 1680s. Until the early 19th century Iowa was occupied exclusively by Native Americans and a few European traders, with loose political control by France and Spain. Iowa became part of the United States of America after the Louisiana Purchase in 1803, but uncontested U.S. control over what is now Iowa occurred only after the War of 1812 and after a series of treaties eliminated Indian claims on the state. Beginning in the 1830s Euro-American settlements appeared in the Iowa Territory, U.S. statehood was acquired in 1846, and by 1860 almost the entire state was settled and farmed by Euro-Americans. Subsistence frontier farming was replaced by commodity farming after the construction of railroad networks in the 1850s and 1860s. Iowa contributed many soldiers who fought in the American Civil War. Afterwards they returned to help transform Iowa into an agricultural powerhouse, supplying food to the rest of the nation. The industrialization of agriculture and the emergence of centralized commodities markets in the late 19th and 20th centuries led to a shift towards larger farms and the decline of the small family farm; this was exacerbated during the Great Depression. Industrial production became a larger part of the economy during World War II and the postwar economic boom. In the 1970s and 1980s a series of economic shocks, including the oil crisis, the 1980s farm crisis, and the Early 1980s recession led to the collapse of commodities prices, a decline in rural and state population, and rural flight. Iowa's economy rebounded in the 1990s, emerging as a modern mixed economy dominated by industry, commerce, and finance, in which agriculture is a comparatively small component. Prehistory in Iowa When the American Indians first arrived (in what is now Iowa) thousands of years ago they would hunt and gather living in a Pleistocene glacial landscape. By the time European explorers visited Iowa, American Indians were largely settled farmers with complex economic, social, and political systems. This transformation happened gradually. During the Archaic period (more than 2,800 years ago), American Indians adapted to local environments and ecosystems, slowly becoming more sedentary as populations increased. More than 3,000 years ago, during the Late Archaic period, American Indians in