In the era of rapid industrialisation after the Napoleonic Wars, nonconformity became firmly established in the new industrial settlements of South Wales as migrants from the rural counties brought their religious affiliations with them.
In places such as Merthyr Tydfil, Aberdare, Llanelli and Neath, Nonconformity grew alongside industry and by the 1880s these towns were regarded as "citadels of dissent", with their ministers and deacons having a powerful role among a new middle class elite which dominated public life.
Professional architects were engaged to design elaborate structures, especially in larger towns such as Aberystwyth, Caernarfon, Carmarthen and Swansea, as well as in the developing townships of the industrial valleys.
The relative absence of these influences in the industrial valleys made Nonconformity even more powerful, especially given that many of the leading coal owners of the late 19th century were Welsh-speaking Nonconformists.
[citation needed] The Congregationalists, usually referred to as the Independents in the Welsh context, were especially strong in south Wales, notably in Carmarthenshire and Glamorgan.
[citation needed] Unitarians flourished in the Teifi Valley in West Wales and also in small pockets in Glamorgan, such as Aberdare.
It is believed that at least 100,000 were involved in the 1904–1905 revival, but historians generally regard it as the last great outpouring of a nonconformist movement that then went into gradual decline, a process exacerbated by the First World War.
The influence of this Act persisted in some parts of Wales until the very late 20th century, with public houses in some counties staying closed on Sundays.
This reflected a close interaction between Nonconformity and temperance movements such as the Good Templars, and "taking the pledge" to abstain from alcohol became a formative part of chapel culture.
Nonconformity was also central to various developments in education, from the post-1870 Board Schools, which in Wales were largely influenced by the chapels, to the first Welsh university established at Aberystwyth in 1872.
Their style was essentially populist, and they enjoyed a spontaneous relationship with their congregations, not only in delivering fiery and often fundamentalist sermons on Sundays but also in popular lectures on figures such as Oliver Cromwell and Garibaldi.