A declining city is one that has been losing its economic base and population over a long period, usually because the industries it was built on, such as mining, steel or shipbuilding, have collapsed and nothing has replaced them.
From the late 1950s, Sweden paid relocation allowances to residents of its declining industrial north who moved south for work. In Bilbao, after the collapse of its steel and shipbuilding industries in the 1980s, the Basque government invested in regeneration, including a new metro, an airport, a river cleanup and the Guggenheim Museum.