When Sino-Japanese War broke out in the summer of 1937, my father just finished his sophomore year at Hosei University, Tokyo, Japan.  He quitted the school and returned to China immediately.  Then there were two roads ahead of him to take on: to KMT Central Military Academy at Nanjing or to CCP Anti-Jap University at Yenan. 

He finally picked Central Military Academy because of the imminence of adverse situation after the loss at Shanghai.  (When he was taking the entrance exam at Nanjing, the Japanese bombers were already hovering over his head.)  Later on he told me there were a lot of other young men like him who were torn between the two choices: Nanjing or Yenan.  But you may ask why did so many young hearts were yearning for a backwater place like Yenan, an underdog like then CCP.  Following reportage may tell you why:

https://www.guancha.cn/xumufeng/2020_08_23_562501_1.shtml