major power vs country

major power and country both are nouns.

Word	Noun	Adjective	Verb	Adverb
major power	Yes	No	No	No
country	Yes	No	No	No

As nouns, country is a hypernym of major power; that is, country is a word with a broader meaning than major power:

major power: a state powerful enough to influence events throughout the world
country: a politically organized body of people under a single government

Other hypernyms of major power include body politic, commonwealth, land, nation, res publica, state.

major power (noun)	country (noun)
a state powerful enough to influence events throughout the world	a politically organized body of people under a single government
	the people who live in a nation or country
	the territory occupied by a nation
	an area outside of cities and towns
	a particular geographical region of indefinite boundary (usually serving some special purpose or distinguished by its people or culture or geography)