The Sierra Leone Civil War (19912002), or the Sierra Leonean Civil War, was a civil war in Sierra Leone that began on 23 March 1991 when the Revolutionary United Front (RUF), with support from the special forces of Charles Taylor's National Patriotic Front of Liberia (NPFL), intervened in Sierra Leone in an attempt to overthrow the Joseph Momoh government. The resulting civil war lasted 11 years, enveloped the country, and left over 50,000 dead.During the first year of the war, the RUF took control of large swathes of territory in eastern and southern Sierra Leone, which were rich in alluvial diamonds. The government's ineffective response to the RUF, and the disruption in government diamond production, precipitated a military coup d'tat in April 1992 by the National Provisional Ruling Council (NPRC). By the end of 1993, the Sierra Leone Army (SLA) had succeeded in pushing the RUF rebels back to the Liberian border, but the RUF recovered and fighting continued. In March 1995, Executive Outcomes (EO), a South Africa-based private military company, was hired to repel the RUF. Sierra Leone installed an elected civilian government in March 1996, and the retreating RUF signed the Abidjan Peace Accord. Under UN pressure, the government terminated its contract with EO before the accord could be implemented, and hostilities recommenced.In May 1997, a group of disgruntled SLA officers staged a coup and established the Armed Forces Revolutionary Council (AFRC) as the new government of Sierra Leone. The RUF joined with the AFRC to capture Freetown with little resistance. The new government, led by Johnny Paul Koroma, declared the war over. A wave of looting, rape, and murder followed the announcement. Reflecting international dismay at the overturning of the civilian government, ECOMOG forces intervened and retook Freetown on behalf of the government, but they found the outlying regions more difficult to pacify.

In January 1999, world leaders intervened diplomatically to promote negotiations between the RUF and the government. The Lome Peace Accord, signed on 27 March 1999, was the result. Lome gave Foday Sankoh, the commander of the RUF, the vice presidency and control of Sierra Leone's diamond mines in return for a cessation of the fighting and the deployment of a UN peacekeeping force to monitor the disarmament process. RUF compliance with the disarmament process was inconsistent and sluggish, and by May 2000, the rebels were advancing again upon Freetown.As the UN mission began to fail, the United Kingdom declared its intention to intervene in the former colony and Commonwealth member in an attempt to support the weak government of President Ahmad Tejan Kabbah. With help from a renewed UN mandate and Guinean air support, the British Operation Palliser finally defeated the RUF, taking control of Freetown. On 18 January 2002, President Kabbah declared the Sierra Leone Civil War over.

The Revolutionary United Front (RUF) was a rebel army that fought a failed eleven-year war in Sierra Leone, beginning in 1991 and ending in 2002. It later transformed into a political party, which still exists today. The three most senior surviving leaders, Issa Sesay, Morris Kallon and Augustine Gbao, were convicted in February 2009 of war crimes and crimes against humanity.