military strength vs capability

military strength and capability both are nouns.

Word	Noun	Adjective	Verb	Adverb
military strength	Yes	No	No	No
capability	Yes	No	No	No

As nouns, capability is a hypernym of military strength; that is, capability is a word with a broader meaning than military strength:

military strength: capability in terms of personnel and materiel that affect the capacity to fight a war
capability: the quality of being capable -- physically or intellectually or legally

Other hypernyms of military strength include capableness.

military strength (noun)	capability (noun)
capability in terms of personnel and materiel that affect the capacity to fight a war	the quality of being capable -- physically or intellectually or legally
	an aptitude that may be developed
	the susceptibility of something to a particular treatment