In mathematics and statistics, the term arithmetic mean is preferred over simply mean because it helps to differentiate between other means such as geometric and harmonic mean. Statistical mean is the most common term for calculating the mean of a statistical distribution.
There were, in my opinion, two main reasons for this: 1  I believe that Dr. King believed that nonviolence was a more moral strategy than one that included violence. 2  King also believed that nonviolence was a more effective way to get people on the side of the protestors.
It ended when Dr. King was assassinated in 1968 -- Dr. King certainly was not the only leader or actor in the Civil Rights Movement. In the '50s and '60s, it was a collection of millions of people around the US and the world who contributed. But, Dr. King was an icon of the movement to many.