The Merthyr Riots
The riots of 1831 were precipitated by a combination of the ruthless collection of debts, frequent wage reductions when the value of iron periodically fell, and the imposition of truck shops. Instead of using normal coin of the realm, some ironmasters paid their workers in specially-minted coins or credit notes, known as "truck". These could only be exchanged at shops owned by the ironmasters. Many of the workers objected to both the price and quality of the goods sold in these company-owned shops.

There is still controversy over what actually happened and who was to blame. It was probably more of an armed rebellion than an isolated riot. The initiators of the unrest were most probably the skilled workers; men who were much prized by the owners and often on friendly social terms with them. They also valued their loyalty to the owners and looked aghast at the idea of forming trade unions to demand higher wages. But events overtook them, and the community was tipped into rebellion.

The owners took fright at the challenge to their authority, and called on the military for assistance. Soldiers were sent from the garrison at Brecon. They clashed with the rioters, and several on both sides were killed. Despite the hope that they could negotiate with the owners, the skilled workers lost control of the movement.

Some 7,000 to 10,000 workers marched under a red flag, which was later adopted internationally as the symbol of the working classes. For four days, they effectively controlled Merthyr.

Even with their numbers and captured weapons, they were unable to effectively oppose disciplined soldiers for very long, and several of the supposed leaders of the riots were arrested. Some were transported as convicts to the penal colonies of Australia. One of them, Richard Lewis, popularly known as Dic Penderyn, was hanged for the crime of stabbing soldier Donald Black in the leg, creating the first local working-class martyr. Alexander Cordell's novel The Fire People is set in this period. A serious political history of these events, The Merthyr Rising was written by the Merthyr-born Marxist and writer Professor Gwyn Alf Williams in 1978.

The first trade unions, which were illegal and savagely suppressed, were formed shortly after the riots. The rising also helped create the momentum that led to the Reform Act. The Chartism movement, which did not consider these reforms extensive enough, was subsequently active in Merthyr.

Many families had had enough of the strife, and they left Wales to utilise their skills elsewhere. Numerous people set out by ship to America, where the steelworks of Pittsburgh were booming. It only cost about five pounds to travel steerage.