Until the late nineteenth century, diamonds were found only in a few riverbeds in India and in the jungles of Brazil, and the entire world production of gem diamonds amounted to a few pounds a year. In 1870, however, huge diamond mines were discovered near the Orange River, in South Africa, where diamonds were soon being scooped out by the ton. Suddenly, the market was deluged with diamonds.
The British financiers who had organized the South African mines quickly realized that their investment was endangered; diamonds had little intrinsic value—and their price depended almost entirely on their scarcity. The financiers feared that when new mines were developed in South Africa, diamonds would become at best only semiprecious gems.
The major investors in the diamond mines realized that they had no alternative but to merge their interests into a single entity that would be powerful enough to control production and perpetuate the illusion of scarcity of diamonds. The instrument they created, in 1888, was called De Beers Consolidated Mines, Ltd., incorporated in South Africa.
Here’s another video .. this one humorous but breaks it down pretty good