It was impossible to have foreseen the changes that industry would bring to Wales in the mid-19th century. While the diggings on the Great Orme (Pen y Gogarth) at Llandudno show that there had been a deal of industrial activity going on since the Bronze Age in that region and elsewhere, it had been small scale and extremely localized. The Romans had extensive quarries for lead and other ores in Flintshire and had sought gold in various locations throughout Wales. They made little impact on the landscape and very little on the social structure of the country. After the middle of the 18th century, however, there was an explosion of mining, quarrying, iron manufacturing and all their related industries.

In northwest Wales, on what was then the green, unspoiled Island of Anglesey, the huge Mona and Parys copper mines helped transform both the economy and the landscape: copper smelting employed hundred of workmen and poisoned the hillsides around Amlwch. Even today, hideous scars remain on now derelict Parys Mountain. In the ancient kingdom of Gwynnedd, also in the northwest, huge quarries began to disfigure the landscape, but also helped employ thousands of men to dig out the slate that roofed houses and municipal buildings throughout Europe.

Today, the mining and manufacture of copper has disappeared. Welsh slate is no longer extensively mined, roofing materials being produced much more efficiently and cheaply elsewhere, though the mountains of waste remain. Elsewhere, the landscape is still being altered immeasurably by monstrous stone quarries to build English roads. Whole mountains near Penmaenmawr are being torn apart in a process that seems to have no end.

Before the end of the 18th century, the Greenfield Valley, below St. Winifred's shrine at Holywell in Flintshire, fed by an ample supply of water, sustained a long line of industrial workings. Copper and brass foundries, supplied by ships brought raw materials from the Thomas Williams mines at Parys Mountain to join the older more traditional woollen and flannel mills. Collieries at nearby Flint and Bagillt; iron foundries at Mostyn, on the Dee estuary; the beginnings of extensive coal mining at Llay, Gresford, and Point of Ayr; and the pioneering John Wilkinson iron works at Bersham, near Wrexham also helped make the Northeast corner of Wales a centre of industry. (A stronghold of the English language long before the area attracted the Merseyside hordes as a place of retirement or holiday homes).

The Seven Years' War of 1756-63, involving most of Europe, accelerated the demand for domestic iron, and all the raw materials necessary for its production were found in a narrow band at the northern edge of the Southeast Wales coalfield. The process of puddling invented by Henry Cort in Hampshire, England in 1783 finally ended the iron industry's reliance on charcoal, at that time in increasingly short supply throughout Britain

The bituminous or semi-bituminous coals of the Welsh Valleys provided a perfect solution: they provided an extremely valuable, readily available fuel in prodigious quantities. Investment capital came mainly from London, bringing in to southeast Wales and influx of experienced iron masters and their workers, mainly from the Midlands, to supply the technical know-how to produce high quality iron.

Other workers flocked in from all parts of Britain, though a large supply came from the farming districts of Carmarthenshire and Cardiganshire. Some of the major iron masters that helped develop Welsh industry were John Guest, associated with the Dowlais and Plymouth works; Anthony Bacon and William Brownrigg, who began the Cyfartha Works; Richard Crawshay, who later bought and expanded Cyfartha; and the Homfrays, who owned Penydarren.

The work of such industrial giants was in great demand, not only during the aforementioned war, but also during the War for American Independence, the Napoleonic Wars and especially for the coming of the railways that were to change Britain (and the world) forever. Professor John Davies has commented that the investment of London bankers in the Welsh iron industry, in at least a dozen large-scale enterprises, was "a concentration of capital in heavy investment without parallel anywhere in the world." And with this investment in industry, of course, came the accompanying investment in methods of transporting the finished products to the waiting ports and ships. By the year 1827, the south Wales iron industry was producing one half of all Britain's iron exports, much of it to the United States.

At the end of the next century, Cardiff would be exporting more coal than any other port in the world, and more than a million people had crowded the valleys that radiated out in the valleys north of the city. South Wales coal was the ideal fuel for the domestic fireplaces of London and other rapidly growing urban centres of England. It also was the preferred fuel for the ever-expanding navies of the world when steam replaced sail and iron replaced wood.

In 1839, to export the vast amounts of coal now reaching the city from the Rhondda Valleys, there was feverish activity to complete the Bute Docks at Cardiff out of the mud in the Severn Estuary. Many impressive fortunes were made from South Wales coal; not all the profits went over the border to England. The foremost coal owner was David Davies of Llandinam who founded the Ocean Coal Company and built a rail link from the coalfields to a purposely-built new port at Barry, near Cardiff.

The rural northwest and central areas of Wales, however, did not share in this growth. They began a process of continually losing people to an increasingly anglicized and urbanized southeast, where iron, coal and tinplate, steel and rails made the area one of the most prolific in the world in terms of industrial production, or to industrial communities in England. The movement into the five great valleys of the South was so great that Wales ranked second to the United States as a world centre of immigration in the latter half of the 19th century.

It was around Merthyr Tydfil (the town of Tydfil the Martyr) that most of the industrial growth in Wales took place. The insatiable demand for iron led the small country village into overtaking Swansea as the largest town in Wales early in the 19th century. It was in the Merthyr district that the great iron works of Cyfartha, Pen y Darren and Blaenavon produced an inordinate share of British Iron, and at Dowlais was made practically the sum total of all iron rails for the fledgling United States railroad industry.

South of Merthyr, and greatly profiting from its heavy industry and relentless toil of its workers, was Cardiff, its outlet to the sea at the bottom of the five valleys (Rhymney, Rhonda, Cynon, Taff, and Ebbw) and the main center of export to the overseas empire. As early as 1794, the two towns were connected by the Glamorgan Canal; two more canals were constructed to link Ebbw Vale with Newport in 1796; and Swansea to its rapidly growing industrial hinterland in 1798. In less than 19 years, by 1839 the Glamorgan Canal alone increased its traffic seven-fold, to 350,000 tons.

By that date, the railways had begun to take over much of the burden of transporting the raw materials to the ports and centres of production: the Taff Vale and the Rhymney were constructed by the middle of the century. It seemed as if everyone would benefit, especially after the discoveries of David Thomas, working under George Crane at the Yniscedwyn Iron Works in Ystradgynlais, in the Swansea Valley, opened up the West Wales coalfield by making it possible to use anthracite coal in the smelting of iron ore.

There were all kinds of problems in the iron and coal industries, and a period of great unrest came to the valleys. This unrest led to their becoming known as one of the premier centres of British radicalism, an unrest that led to a particular Welsh kind of political activity and that, in time, would lead to a socialist-thinking, Labour-voting electorate that was still predominant in the 1990's. The Merthyr Rising began in 1831; for the people of Wales it was a new struggle, of a different kind true, but a struggle as intense as any that had gone before.