Q: Passage: The Sierra Leone Civil War (1991 -- 2002) 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.

Question: Based on this passage, when did the war start in sierra leone? Let's give stream of consciousness first:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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The important part for answering this question is: The Sierra Leone Civil War (1991 -- 2002) 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. Therefore, the final answer is 1991.