Steady increases in output and manpower meant that the early 20th century gave Wales its peak production figures.
No less than 57m tons of coal was produced in 1913, by 232,000 men working in 620 mines.
The largest number of men ever to work in the Welsh coal mines was 271,000 in 1920.
Post war, there was a recession in the coal market, due to a combination of a move to oil power by shipping and the development of coal industries overseas.
Men were laid off: 140,000 by 1936. South Wales lost 241 mines in the same period.
World War Two didn't buck the trend in terms of production, but indirectly it had the effect of instilling some optimism. The Labour government of 1945 - the Welfare State government - nationalised the coal industry on 1 January 1947, taking it out of the hands of private firms.
It was thought that this move would safeguard jobs and mines, as the government would be less likely than private owners to cut and run or make a quick sale.
At the time, there were still 135 collieries with over 250 workers each and, although exports through Cardiff had fallen from 25m tons in 1913 to 750,000 tons in 1947, there was much needed modernisation and investment coming.
Investment meant better and more machinery and a greater emphasis on safety, but couldn't safeguard the coal industry in Wales.
The rise of the oil industry and other factors meant that 50 collieries closed in south Wales between 1957 and 1964. Although there was some respite in the 1970s due to the oil crisis, by the 1980s it was almost all over for the coal industry in Wales and the rest of the UK.
A last gasp of industrial action, the 1984 miners' strike, was not enough to prevent the death of an industry that was once the biggest single employer in Wales and held the most powerful workforce.
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