*Disclaimer: I'm just an average American. Not a teacher, grammar expert, or language expert. Very impressive! Some recommendations: My textbook told me that (1), in the meantime, (2) the Republic of China was slowing down (3) Axis Japan in the (4) Eastern war field. 1) This is complex punctuation in English. I'd put a comma here because the sentence is acceptable without the part *in the meantime*. Such as: My textbook told me that the Republic of China... It also indicates a small pause in speech. Imagine speaking it, My textbook told me that *small pause* in the meantime *small pause* ... 2) When we have the word 'republic' in a country name, it needs to have 'the' in it. Examples: The Republic of China The Dominican Republic The Czech Republic 3) I removed 'the' since 'Axis Japan' is referring to a country without 'Republic' in it. 4) This one is difficult to explain. In *most* (not all - so many exceptions lol) cases, [North, East, South, West] are used as nouns. Whereas [Northern, Eastern, Southern, Western] are used as adjectives. In your sentence, the war field is the noun so I would use 'Eastern' to describe it. Also, it just *sounds* better to me.

Thank you for your corrections. Thank you👍