By the early 1980s, many pits were almost 100 years old and were considered uneconomic to work at current wage rates compared to cheap North Sea oil and gas, and in comparison to subsidy levels in Europe. The Miners' Strike of 1984 failed to stop the Conservative government's plans under Margaret Thatcher to shrink the industry, and a break-away Union of Democratic Mineworkers was founded by miners, mostly in the Midlands, who felt that the NUM had broken its own democratic rules in calling the strike. The National Coal Board (by then British Coal), was privatised by selling off a large number of pits to private concerns through the mid-1990s. Because of exhausted seams, high prices and cheap imports, the mining industry disappeared almost completely, despite the militant protests of some miners.