i'm just like you. but I know later on:
KMT/ Kou Ming Tang : Chinese nationalists (Ming Tai and Wang Tian Feng's side).
Communist: Chinese nationalists too (nationalist here i'm not sure but I mean the broad term like whoever love their country sometimes they sound extreme)
~note~ KMT and Communists fight the Japanese and New government. So KMT and the Communists have a common enemy here. They can or might work together later on.
Japanese: They work with the New Government.
New Government: Chinese work under Japanese (A.K.A Wang Man Chun, Liang Zhong Chun's side)
Side Note: this is my first drama about this topic and era and I rolled my eyes when lead characters say "country before family" speeches. I find that too extreme, makes me feel awkward, almost sounds like a propaganda show, but probably around that time/era speeches like that is realistic. My benefit of the doubts is that the director of this drama wants it to be realistic.