The service industry is the largest economic contributor in South Dakota. This sector includes the retail, finance, and health care industries. Citibank, which was the largest bank holding company in the United States at one time, established national banking operations in South Dakota in 1981 to take advantage of favorable banking regulations. Government spending is another important segment of the state's economy, providing over ten percent of the gross state product. Ellsworth Air Force Base, near Rapid City, is the second-largest single employer in the state.