combat area vs war zone

combat area and war zone both are nouns.

Word	Noun	Adjective	Verb	Adverb
combat area	Yes	No	No	No
war zone	Yes	No	No	No

As nouns, war zone is a hyponym of combat area; that is, war zone is a word with a more specific, narrower meaning than combat area:

combat area: a military area where combat forces operate
war zone: a combat zone where military operations are coordinated (especially a designated area in international waters where the rights of neutrals are not respected by nations at war)

Other hyponyms of combat area include bridgehead, foothold.

combat area (noun)	war zone (noun)
a military area where combat forces operate	a combat zone where military operations are coordinated (especially a designated area in international waters where the rights of neutrals are not respected by nations at war)