In the beginning, the diamond trade took place mostly in India and Brazil. With the discovery of diamonds in South Africa, the trade simultaneously took off and become much less profitable

Premier Diamond Mine, South Africa Wikimedia

Up until the mid-1800s, diamonds were a rarity and could be seen only on the hand of a monarch. But the diamond rush that began in South Africa in the second half of the 19th century flooded the market with diamonds, which, as any good businessman knows, kills demand.

It would take some ingenious plotting and advertising to keep the diamond's reputation as intrinsically valuable and desirable, which is where De Beers comes in