Which group united in 1890 to coordinate diamond sales among major producers?

The London Diamond Syndicate was established in 1890 specifically to coordinate diamond sales among major producers. This organization was formed to create a consolidated effort among the key players in the diamond industry, allowing them to manage the supply and demand effectively and maintain stable pricing in the market. By operating in this way, the syndicate aimed to protect the interests of diamond producers and foster industry cooperation.

In contrast, other groups listed in the options, such as the Diamond Trade Alliance and the Global Diamond Council, do not have the same historical significance or focus on the coordination of sales among major producers as the London Diamond Syndicate. The Federation of Diamond Producers also does not align with the specific context of the 1890 founding and coordination of diamond sales. Thus, the choice of the London Diamond Syndicate reflects its key role in the history of diamond trade coordination.