military strength vs military capability

military strength and military capability both are nouns.

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

As nouns, military strength and military capability are synonyms defined as:

military strength and military capability: capability in terms of personnel and materiel that affect the capacity to fight a war

Other synonyms of military strength include military posture, posture, strength.

military strength (noun)	military capability (noun)
capability in terms of personnel and materiel that affect the capacity to fight a war	capability in terms of personnel and materiel that affect the capacity to fight a war