military capability vs military strength

military capability and military strength both are nouns.

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

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

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

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

military capability (noun)	military strength (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