There are two reasons for viewing the development of electricity as one of the key issues of economic organisation in the 1914–50 period. In the late nineteenth century, electricity suppliers found the gas industry a tough competitor, and electricity was characterised in chapter 5 as a largely local affair, involving municipalities and small companies, albeit with signs of major developments in industrial uses. By the early decades of the twentieth century, long-distance electricity transmission lines were being constructed, and by the end of the First World War, the potential economic and strategic benefits of interconnected supply systems, stretching over whole regions and countries, had become a key technological reason for government involvement in industrial organisation. A new infrastructure track was being built, which carried even bigger economies of scale than the railways. Once a transmission line was laid, the actual business of transmitting electricity involved hardly any operating costs; the main running ‘costs’ were energy losses. The benefits from interconnection seemed huge. A second factor was the extension in the use of electricity. In the first half of the twentieth century, coal was still king as an energy source. New sources – oil, natural gas and water power – were emerging, and nuclear was to follow in the near future. They accounted for 3% of Europe's consumption of primary energy in 1920. By 1938 this figure had risen to only 5%.