Karlstad (kärlˈstäd) [key], city (1990 pop. 52,930), capital of Värmland co., S Sweden, on Lake Vänern. It has ironworks and machine shops and other industries that manufacture forest products and heavy machinery. Known as Thingvalla (or Tingvalla) in the Middle Ages, it was chartered by Charles IX as Karlstad in 1584. A fire in 1865 destroyed much of the city. The treaty that severed the union of Norway and Sweden was negotiated and signed there in 1905.