 The effect on British coal mines was profound.By the late 1930s, employment in mining had fallen by more than a third from its pre-strike peak of 1.2 million miners, but productivity had rebounded from under 200 tons produced per miner, to over 300 tons by the outbreak of the Second World War.The split in the miners that resulted from Spencerism and the agreement of the Nottinghamshire miners to return to work, against the policy of the Miners' Federation of Great Britain divided the coal miners as a national bargaining force until the establishment of the National Union of Mineworkers.