nuclear club vs assemblage

nuclear club and assemblage both are nouns.

Word	Noun	Adjective	Verb	Adverb
nuclear club	Yes	No	No	No
assemblage	Yes	No	No	No

As nouns, assemblage is a hypernym of nuclear club; that is, assemblage is a word with a broader meaning than nuclear club:

Other hypernyms of nuclear club include accumulation, aggregation, collection.

nuclear club (noun)	assemblage (noun)
the nations possessing nuclear weapons	the social act of assembling
	a system of components assembled together for a particular purpose
	a group of persons together in one place
	several things grouped together or considered as a whole