I don't think anyone ever had an entirely conflict-free engagement, but you can get a conflict-free diamond, and you should. According to Amnesty International "diamonds have been, and continue to be linked to terrible human rights abuses either by insurgent groups to fuel conflict and carry out atrocities against innocent civilians or by unscrupulous governments who are equally brutal." Currently in place is something called the Kimberley Process, which is supposed to "protect the legitimate diamond industry and consumers from purchasing tainted stones" . However, Amnesty and other human rights groups don't think the KP goes far enough. There are still thousands of conflict diamonds sold every year, which are used to "fuel civil wars and human rights abuses." Globalwitness.org, reports that conflict diamonds have funded the weapons purchases of warlords and rebels in Africa. According to their website, " An estimated 3.7 million people have died in Angola, the Democratic Republic of the Congo, Liberia, and Sierra Leone in conflicts fuelled by diamonds."
The chances are very small that a jeweler here in the US would sell you a conflict-diamond. Because of the Kimberley Process, jewelers are only allowed to import certified conflict-free stones. However, that doesn't mean it never happens, black market and smuggled diamonds do find their way into mainstream jewelry stores. So what can you do to be SURE that you're not buying a conflict diamond? Ask your jeweler to show you a written guarantee from their diamond suppliers stating that their diamonds are conflict-free. If they don't know what you're talking about, or can't supply a written document for you, go somewhere else, and tell them why. They should be more than happy to help. For more information about conflict-free diamonds, see:
Amnesty International
Buyer's Guide