Prior to the British Industrial Revolution there were small-scale industries scattered throughout Wales. These ranged from those connected to agriculture, such as milling and the manufacture of woollen textiles, through to mining and quarrying. Agriculture remained the dominant source of wealth. The emerging industrial period saw the development of copper smelting in the Swansea area. With access to local coal deposits and a harbor that connected it with Cornwall’s copper mines in the south and the large copper deposits at Parys Mountain on Anglesey, Swansea developed into the world’s major center for non-ferrous metal smelting in the 19th century. The second metal industry to expand in Wales was iron smelting, and iron manufacturing became prevalent in both the north and the south of the country. In the north, John Wilkinson‘s Ironworks at Bersham was a major center, while in the south, at Merthyr Tydfil, the ironworks of Dowlais, Cyfarthfa, Plymouth and Penydarren became the most significant hub of iron manufacture in Wales. By the 1820s, south Wales produced 40 per cent of all Britain’s pig iron.
In the late 18th century, slate quarrying began to expand rapidly, most notably in north Wales. The Penrhyn Quarry, opened in 1770 by Richard Pennant, was employing 15,000 men by the late 19th century, and along with Dinorwic Quarry, it dominated the Welsh slate trade. Although slate quarrying has been described as “the most Welsh of Welsh industries”, it is coal mining which became the industry synonymous with Wales and its people. Initially, coal seams were exploited to provide energy for local metal industries but, with the opening of canal systems and later the railways, Welsh coal mining saw an explosion in demand. As the South Wales coalfield was exploited, Cardiff, Swansea, Penarth and Barry grew as world exporters of coal. By its height in 1913, Wales was producing almost 61 million tons of coal.
Historian Kenneth Morgan described Wales on the eve of the First World War as a “relatively placid, self-confident and successful nation”. The output from the coalfields continued to increase, with the Rhondda Valley recording a peak of 9.6 million tons of coal extracted in 1913. The First World War (1914–1918) saw a total of 272,924 Welshmen under arms, representing 21.5 per cent of the male population. Of these, roughly 35,000 were killed, with particularly heavy losses of Welsh forces at Mametz Wood on the Somme and the Battle of Passchendaele. The first quarter of the 20th century also saw a shift in the political landscape of Wales. Since 1865, the Liberal Party had held a parliamentary majority in Wales and, following the general election of 1906, only one non-Liberal Member of Parliament, Keir Hardie of Merthyr Tydfil, represented a Welsh constituency at Westminster. Yet by 1906, industrial dissension and political militancy had begun to undermine Liberal consensus in the southern coalfields. In 1916, David Lloyd George became the first Welshman to become Prime Minister of Britain. In December 1918, Lloyd George was re-elected at the head of a Conservative-dominated coalition government, and his poor handling of the 1919 coal miners’ strike was a key factor in destroying support for the Liberal party in south Wales. The industrial workers of Wales began shifting towards the Labour Party. When in 1908 the Miners’ Federation of Great Britain became affiliated to the Labour Party, the four Labour candidates sponsored by miners were all elected as MPs. By 1922, half the Welsh seats at Westminster were held by Labour politicians—the start of a Labour dominance of Welsh politics that continued into the 21st century.