Complex sentence: During the Long March, Ye assisted Liu Bocheng in directing the crossing of the Yangtze River at Anshunchang and Luding Bridge, and became director of the offices that liaised with the KMT after 1936, first in Xi'an, then in Nanjing and finally in Chongqing.
Split into simpler sentences: During the Long March, Ye assisted Liu Bocheng in directing the crossing of the Yangtze River at Anshunchang and Luding Bridge. After 1936, Ye became director of the offices that liaised with the KMT, first in Xi'an, then in Nanjing and finally in Chongqing.