The coal mining industry of the Valleys was buoyed throughout World War II, though there were expectations of a return to the pre-1939 industrial collapse after the end of the war. There was a sense of salvation when the government announced the nationalisation of British coalmines in 1947; but the following decades saw a continual reduction in the output from the Welsh mines. The decline in the mining of coal after World War II was a country-wide issue, but southern Wales was more severely affected than other areas of Britain. Oil had superseded coal as the fuel of choice in many industries, and there was political pressure influencing the supply of oil. Of the few industries that still relied on coal, the demand was for quality coals, especially coking coal, which was required by the steel industry. Fifty percent of Glamorgan coal was now supplied to steelworks, with the second biggest market being domestic heating, in which the "smokeless" coal of the southern Wales coalfield again became fashionable after the Clean Air Act of 1956 was passed. These two markets now controlled the fate of the mines in Wales, and as demand from both sectors fell, the mining industry contracted further. In addition exports to other areas of Europe, traditionally France, Italy and the Low Countries, experienced a massive decline: from 33% around 1900 to roughly 5% by 1980.