A slight disclaimer - you'll notice the artical is from a long time ago - De Beers have threatened and bullied their way through their history and guess where Nazi Germany got industrial diamonds from to keep their war machine going.
In fact they were so bad that US anti-trust legislaton meant that they could not operate in the US and all of New Yorks diamond merchants used to have to fly over monthly to London to see what stock they'd been allocated - and heaven help them if they complained about what they got.
Then 2 years ago they made peace with the US government, paid a $10 million fine and were allowed to operate there again.
At the moment the big threat to them is artificially made diamonds so good you need special equipment to distinguish them. People like this:
http://www.diamondnexuslabs.com/?utm_id=11&gcl id=CM_3nNqZmYgCFTZREgod03lSXA
They are real diamonds just made in a lab - De Beers' response has been 2 pronged - on one hand to sneer at them with a kind of "would you honestly give your fiance a "fake" diamond kind of message whilst on the other hand setting their larger stones with trademarks and serial numbers so that they can always distinguish them.
Whether they continue to play above board or revert to type we'll see.
Incidently a 2 carat man made diamond ring from Nexus is $431as opposed to $9,000
It might be a really interesting alternative