The need to maintain coal supplies (a primary energy source) had figured in both world wars. As well as energy supply, coal became a very political issue, due to conditions under which colliers worked and the way they were treated by colliery owners. Much of the 'old Left' of British politics can trace its origins to coal-mining areas, with the main labour union being the Miners' Federation of Great Britain, founded in 1888. The MFGB claimed 600,000 members in 1908. (The MFGB later became the more centralised National Union of Mineworkers).