The U.S. state of Kansas, located on the eastern edge of the Great Plains, was the home of nomadic Native American tribes who hunted the vast herds of bison (often called "buffalo"). In around 1450 AD, the Wichita People founded the great city of Etzanoa. The city of Etzanoa was abandoned in around 1700 AD. The region was explored by Spanish conquistadores in the 16th century. It was later explored by French fur trappers who traded with the Native Americans. Most of Kansas became permanently part of the United States in the Louisiana Purchase of 1803. When the area was opened to settlement by the Kansas–Nebraska Act of 1854 it became a battlefield that helped cause the American Civil War. Settlers from North and South came in order to vote slavery down or up. The free state element prevailed. After the war, Kansas was home to frontier towns; their railroads were destinations for cattle drives from Texas. With the railroads came heavy immigration from the East, from Germany as well as some freedmen called "Exodusters". Farmers first tried to replicate Eastern patterns and grow corn and raise pigs, but they failed because of shortages of rainfall. The solution, as James Malin showed, was to switch to soft spring wheat and later to hard winter wheat. The wheat was exported to Europe and was subject to wide variations in price. Many frustrated farmers joined the Populist movement around 1890, but conservative townspeople finally prevailed politically. They supported the progressive movement down to about 1940, but isolationism in foreign affairs combined with prosperity for the farmers and townsfolk made the state a center of conservative support for the Republican Party since 1940. Since 1945 the farm population has sharply declined and manufacturing has become more important, typified by the aircraft industry of Wichita. Prehistory The Paleo-Indians and Archaic peoples Around 7000 BC, paleolithic descendants of Asian immigrants into North America reached Kansas. Once in Kansas, the indigenous ancestors never abandoned Kansas. They were later augmented by other indigenous peoples migrating from other parts of the continent. These bands of newcomers encountered mammoths, camels, ground sloths, and horses. The sophisticated big-game hunters did not keep a balance, resulting in the "Pleistocene overkill", the rapid and systematic destruction of nearly all the species of large ice-age mammals in North America by 8000 BC. The hunters who pursued the mammoths may have represented the first