mines exceeded one million carats per year. As production increased, those of lesser means were able to join in on this movement. However, diamond engagement rings were for a long time seen as the domain of the nobility and aristocracy, and tradition often favoured simpler engagement bands. In 1852, the ‘Kohinoor’ diamond was re-cut and embellished in Queen Victoria’s crown. This triggered a diamond rush throughout the world. 20th century In the United States, the popularity of diamond engagement rings declined after World War I, even more so than after the onset of the Great Depression. In 1938, the diamond cartel De Beers began a marketing campaign that would have a major impact on engagement rings. During the Great Depression of the 1930s, the price of diamonds collapsed. At the same time, market research indicated that engagement rings were going out of style with the younger generation. Before World War II, only 10% of American engagement rings contained a diamond. While the first phase of the marketing campaign consisted of market research, the advertising phase began in 1939. One of the first elements of this campaign was to educate the public about the 4 Cs (cut, carats, color, and clarity). In 1947 the slogan "a diamond is forever" was introduced. Ultimately, the De Beers campaign sought to persuade the consumer that an engagement ring is indispensable, and that a diamond is the only acceptable stone for an engagement ring. The sales of diamonds in the United States rose from $23 million to $2.1 billion between 1939 and 1979. Law professor Margart F. Brining links the surge in engagement ring sales in the USA after 1945 to the abolishment of the "breach of promise", that had entitled a woman whose fiancé had broken off their engagement to sue him for damages. This rule of law was especially important for many women who had been sexually intimate with the fiancé, but were socially expected to be virgins in a new marriage, therefore lost "market value". After the gradual abolishment of that law action in all states the expensive engagement ring rose to popularity as a new financial security in case of a break-up, since it was custom for the women to keep the ring (partly only under the condition that the break-up was not seen as her fault). 21st century In the early 21st century, the jewellery industry started marketing engagement rings