Complex sentence: They also write that Chiang Kai-shek allowed the Communists to proceed without significant hindrance, and even provided them with maps as his son was being held hostage in Moscow and that he feared he would be killed if the Communists were crushed.
Split into simpler sentences: They also write that Chiang Kai-shek allowed the Communists to proceed without significant hindrance. They provided the communists with maps and allowed them to escape the clutches of his army because his son was being held hostage in Moscow and he feared he would be killed if the Communists were crushed.