i have placed references after the paragraphs, if you want to read more into it.
Conflict diamonds captured the world's attention during the extremely brutal conflict in Sierra Leone in the late 1990s. During this time, it is estimated that conflict diamonds represented approximately 4% of the world's diamond production. Illicit rough diamonds have also been used by rebels to fund conflicts in Angola, Liberia, Ivory Coast, the Democratic Republic of Congo and the Republic of Congo
In July 1999, following over eight years of civil conflict, negotiations between the Government of Sierra Leone and the Revolutionary United Front led to the signing of the Lome Peace Agreement under which the parties agreed to the cessation of hostilities, disarmament of all combatants and the formation of a government of national unity.
http://www.un.org/peace/africa/Diamond.html
A diamond merchant shows his wares June 15, 2001 in Kenema, Sierra Leone. Muslim militant Osama bin Laden's al Qaeda network has collected millions of dollars from the illicit sale of diamonds mined by Revolutionary United Front (RUF) rebels in Sierra Leone. © Chris Hondros/Getty Images.
While the wars in Angola and Sierra Leone are now over, and fighting in the DRC has decreased, the problem of conflict diamonds hasn't gone away. Diamonds mined in rebel-held areas in Côte d'Ivoire, a West African country in the midst of a volatile conflict, are reaching the international diamond market. Conflict diamonds from Liberia are also being smuggled into neighboring countries and exported as part of the legitimate diamond trade.
http://www.amnestyusa.org/Our_Issues/Conflict_Diamonds/page.do?id=1011014&n1=3&n2=74
Sierra Leone
The economic and social infrastructure of Sierra Leone is not well developed. Around two thirds of the population survive by subsistence agriculture, although alluvial diamond mining (mining that extracts diamonds from deposits of sand, gravel and clay, which have been naturally transported by water erosion and deposited along either the banks of a river, the shoreline or on the bed of the ocean) accounts for nearly half of the country's exports and is the most significant source of hard currency earnings.
Diamonds were first discovered in Sierra Leone in 1930. In addition to diamonds, the country also has several other natural resources - titanium ore, bauxite, iron ore, gold and chromite.
Between 1991 and 2002, the country suffered a brutal, ten-year civil war during which the Revolutionary United Front (RUF) committed horrendous atrocities, terrorizing the population and gaining control of the country's diamond mines.
Eight years of protracted war left tens of thousands of people displaced and unknown numbers dead or mutilated. Half a million of Sierra Leone's people were forced to flee the country. The UN Security Council established the Mission in Sierra Leone (UNAMSIL) in October 1999 to help restore peace. At its height, UNAMSIL had 17,000 troops and was the biggest UN peacekeeping operation in the world. The Abuja Agreement in 2001 finally led to a reduction of hostilities and by early 2002, tens of thousands of ex-combatants had been disarmed and demobilized. By January of 2002, the civil war was over and Sierra Leone became a democratic country.
http://www.diamondfacts.org/conflict/background.html#sierra