Black Force(Sa-Pa or Dark Path in early translation) is one of the four forces in the Manhwa. Cheon Ma Sin Gun is said to be the leading figure of Black Force.
In the beginning, when there were only three known forces, Black Force and White Force are said to be at war. For the past 50 years under the lead of Cheon Ma Sin Gun, Black Force was able to push back White Force. The guild that put a stop to Black Force advance was the Song Mu Guild. After a bloody battle with heavy losses on both side, with the death of Song Mu's guild master the conquering came to a halt. Many guild of the Black Force are still waiting for Cheon Ma Sin Gun to once again lead them to destroy White Force for good and unify Murim.
The duel between Han Bi Kwang and Chun Oon-ak almost result in a new war between White Force and Black Force. This battle result in the present of many great figures from White Force, Black Force but also Neutral Force.
However, when Sinji was made known, many clan of Black Force has already defect to Sinji. After Sinji was put into light the two Forces, White Force and Black Force joined their forces and march toward Sinji.