Why did Mao start the long march?

He was retreating (aka running away) from the KMT army, who's army was much bigger and much better trained. the KMT aided by Warlords in the area were slowely encircling the CCPs position. The CCP were not getting the supplize they needed and knew that if they did not move they would either starve or be killed by the KMT army. the march ended in Yan'an