(Peter) Waldo, as it happens, was a well off merchant in France who, in 1173, gave away all his property and began preaching a life of poverty as a means to true perfection. In particular this put him in contrast with the wealth of the Catholic clergy. Waldo did not stop there, however, and between 1175 and 1185 Waldo either translated or had translated a version of the New Testament in the local language of Lyon. To make matters even worse he taught that the concept of purgatory was an "invention of the Antichrist." Waldo was a Protestant before Protestants were cool.
Needless to say this put him and his followers at odds with the Catholic church.
Through a long and complicated history the Waldensians became the target of Church persecution. They were officially declared heretics (teachers of false doctrine) in 1184 and by the mid-1180s they were excommunicated (meaning, as far as the Church in Rome was concerned, they were going to Hell). It did not stop there, in 1211 80 were burned as heretics. In 1487 Pope Innocent the VIII issued a papal bull calling for their extermination, which motivated a short crusade that almost completely wiped them out.
The majority that survived fled to the mountains of Northern Italy and there remained in hiding until the Protestant Reformation. They eventually emerged as a Protestant church, finding common cause with the followers of Zwingly and Calvin. Not that it did them many favors.
The Massacre of Mérindol took place in 1545, when Francis I of France ordered the Waldensians of the city of Mérindol to be punished for dissident religious activities. Provençal and Papal soldiers killed hundreds or even thousands of Waldensian villagers. In January 1655 the Duke of Savoy ordered the Waldensians there to either attend Mass or withdraw into the mountains, in the middle of winter, which the vast majority of them chose to do. Seeing his efforts fail to convert them, on Easter of the same year he ordered his troops in just before dawn and massacred about 1700 of them. In 1685 the French king revoked religious protection for them and sent his troops to "convert" them, which about 9000 did while another 3000 fled to Germany. Later that same year 8000 would be imprisoned and 2000 killed by the Duke of Savoy. However this time guerrilla fighters eventually won the release of the prisoners a few months later. It wouldn't be until 1848 that the Waldensians would receive any kind of formal civil rights under the law in France and Italy (or rather the kingdoms as they were then).
The above supplied just in case you were wondering what religious persecution ACTUALLY looks like.