What led to the crusades

Many factors led to crusades: some participants wanted to gain more prestige among other warriors, get rich (by plundering the lands on the way), some wanted to have support from the Pope, Bishops and the Church for their local issues.
Some truly believed in the cause.
The direct reason was a call from the Pope. 

The median is 4 because 2 x’s out 9, 3 x’s out 7, 3 x’s out 5, and 4 is the only remaining number.