The proximate cause of the 1984–85 miners' strike, the longest mass strike in British history, was a round of colliery closures announced by the National Coal Board (NCB, now British Coal) in March 1984 as part of the restructuring of the British coal mining industry. The impact of pit closures upon communities is so immediate and devastating that the effect obscured the fundamental causes. The restructuring process had accelerated since 1979 because of the economic and energy policies adopted by Conservative governments, but had its origins in the Labour government's response to the 1973 oil shock and the tripartite settlement of the 1974 strike by the National Union of Mineworkers (NUM). The 1974 Plan for Coal established an investment programme to expand coal production by three means: developing new mines; extending the life of existing collieries; and implementing new technologies. These supply-side measures were already underway when the first Thatcher government, elected in 1979, established new limits on publicsector spending and sought to liberalize markets.