Catharism
The Cathars are separated into two groups: the perfects and the believers. There are higher expecations for the perfects than the believers to live up to the moral standards for the Cathars. To become a perfect, the believers take part in a sacrament called the consolamentum, which removes the sins from the believers and can only be done once. This sacrament is usually performed when the believers are near death because this shortens the amount of time in which they must take on the pressures of always acting perfectly. Since the perfects are expected to die soon, they are usually starved or smothered to quicken their deaths. This process is called endura.
Catharism decries several of the beliefs and practices of the Catholic Church (such as the Eucharist and Baptism by water), which enraged the Catholic Church. Angered by the murder of his legate, Pope Innocent III called for a crusade (called the Albigensian Crusade, which lasted from 1209 to 1229) against the Cathars. He made a deal with the French, in which any French noble who fights against the Cathars is able to take their land. In the first attack, crusaders went to the city of Béziers where they killed everyone, including the Catholics, and burned the entire city to the ground. The successes of the crusaders continued until 1215 when resistance for the Albigensians consolidated and started revolting and taking back their land. From 1225 until 1229, Louis VIII and Louis IX took over the crusade. They made a deal with Raymond, a leader of the Albigensian resistance, to end the crusade. In 1234, the Inquisition was created to eradicate the remaining Cathars; this succeeded in killing the Catharism movement and pushing the few Cathars left into hiding.
Interesting Fact: The Cathars believe that the members reincarnate until they manage to give up worldly pleasures. They also believe that the spirit is genderless, so men can reincarnate as women and vice versa. Due to this reincarnation belief, Cathar women are given more power. They can be perfects and even leaders in their communities.
http://www.britannica.com/topic/Cathari
http://www.cathar.info/
https://en.wikipedia.org/wiki/Catharism
https://en.wikipedia.org/wiki/Albigensian_Crusade