military action vs war

military action and war both are nouns.

Word	Noun	Adjective	Verb	Adverb
military action	Yes	No	No	No
war	Yes	No	Yes	No

As nouns, war is a hyponym of military action; that is, war is a word with a more specific, narrower meaning than military action:

military action (noun)	war (noun)
a military engagement	the waging of armed conflict against an enemy
	a concerted campaign to end something that is injurious
	an active struggle between competing entities
	a legal state created by a declaration of war and ended by official declaration during which the international rules of war apply

military action (verb)	war (verb)
	make or wage war