The big question is why?
The Revolutionary United Front fought for years in an unsuccesful insurrection in Sierra Leone.The RUF did not start as a terror group.It basically started to overthrow the then present government.It later developed into a political party.
When it began it's slogan was,"No More Slaves, No More Masters. Power and Wealth to the People"
However the RUF gave no idea about what type of government it would form.They did not advocate Marxism or any similar leftist ideology.
The real reason for the formation of RUF was to overthrow the present government because of certain objections to their policies.
Although the RUF began as a small rebel party,later on it became one of the most terrorising rebel groups of the modern world.
The RUF had very few supporters once they turned into a terrorising party.Although they continued receiving support from across the border,especially from pro RUF units based in Liberia.So they resorted to diamond trading so as to finance the war against the government.
Over the course of years they emerged successful in this attempt.
The diamond were smuggled to Liberia and were legally exported from there.The RUF during this whole process received millions of dollars as price for the diamonds.
So that is why they resorted to the blood diamond trade so as to finance the war against the government.