What happened to cause chinese communists to undertake the long march in 1933

The correct answer to this open question is the following.

What caused Chinese Communists to undertake the Long March in 1933 was the following. The Chinese Communists led by Mao Zedong retreated in October 1934. China was living the Civil War years in which Communists troops fought the Nationalist army.  The Long March of the Communist Army lasted one year. The Communist army retreated by night and had to suffer many calamities and deaths. So the retreat was what caused the Long March to evade the persecution and pursue of the Nationalist troops.