Until the mid-nineteenth century, the South Wales valleys were lightly inhabited. The industrialisation of the Valleys occurred in two phases. First, in the second half of the 18th century, the iron industry was established on the northern edge of the Valleys, mainly by English entrepreneurs. This made South Wales the most important part of British ironmaking until the middle of the 19th century. Second, from 1850 to the outbreak of the First World War , the South Wales Coalfield was developed to supply steam coal and anthracite .