Other theory says that Sati began with a jealous queen who...

Other theory says that Sati began with a jealous queen who heard that dead kings were welcomed in heaven by hundreds of beautiful women, called Apsaras. And therefore when her husband died, she demanded to be burnt on her dead husband's pyre and so to arrive with him to heaven and this way to prevent the Apsaras from consorting with her husband. There are also other theories about the origins of Sati.

Even though Sati is considered an Indian custom or a Hindu custom it was not practiced all over India by all Hindus but only among certain communities of India. On the other hand, sacrificing the widow in her dead husband's funeral or pyre was not unique only to India. In many ancient communities it was an acceptable feature. This custom was prevalent among Egyptians, Greek, Goths, Scythians and others.

Among these communities it was a custom to bury the dead king with his mistresses or wives, servants and other things so that they could continue to serve him in the next world. Another theory claims that Sati was probably brought to India by the Scythians invaders of India. When these Scythians arrived in India, they adopted the Indian system of funeral, which was cremating the dead.

And so instead of burying their kings and his servers they started cremating their dead with his surviving lovers. The Scythians were warrior tribes and they were given a status of warrior castes in Hindu religious hierarchy. Many of the Rajput clans are believed to originate from the Scythians. Later on other castes who claimed warrior status or higher also adopted this custom.

This custom was more dominant among the warrior communities in north India, especially in Rajasthan and also among the higher castes in Bengal in east India. Among the Rajputs of Rajasthan, who gave lot of importance to valor and self sacrifice, wives and concubines of the nobles even committed suicide, when they came to know that their beloved died in battlefield. In other parts of India it was comparatively low. And among the majority of Indian communities it did not exist at all.

A few rulers of India tried to ban this custom. The Mughals tried to ban it. The British, due to the efforts of Hindu reformers like Raja Ram Mohan Roy outlawed this custom in 1829. There aren't exact figures about the number of Sati incidences. In general, before this custom was outlawed in 1829, there were a few hundred officially recorded incidences each year.