Northumberland role in the Industrial Revolution from the 18th century on. Many coal mines operated in Northumberland until the widespread closures in the 1970s and 1980s. Collieries operated at Ashington, Bedlington, Blyth, Choppington, Netherton, Ellington and Pegswood. The region's coalfields fuelled industrial expansion in other areas of Britain, and the need to transport the coal from the collieries to the Tyne led to the development of the first railways. Shipbuilding and armaments manufacture were other important industries before the deindustrialisation of the 1980s. Northumberland remains largely rural, and is the least-densely populated county in England. In recent years the county has
County (United States) Atoll, Kingman Reef, and Navassa Island. The remaining 3 islands in the U.S. Minor Outlying Islands have small non-permanent human populations. The least populous county-equivalent with a permanent human population is Swains Island, American Samoa (17 residents). The most densely populated county or county-equivalent is New York County, New York (coextensive with the New York City Borough of Manhattan), with 72,033 persons per square mile (27,812/km) in 2015. The Yukon-Koyukuk Census Area, Alaska, is both the most extensive and the least densely populated county or county-equivalent with 0.0380 persons per square mile (0.0147/km) in 2015. In the 50 states (plus