Third World vs assemblage

Third World and assemblage both are nouns.

Word	Noun	Adjective	Verb	Adverb
Third World	Yes	No	No	No
assemblage	Yes	No	No	No

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

Third World: underdeveloped and developing countries of Asia and Africa and Latin America collectively
assemblage: several things grouped together or considered as a whole

Other hypernyms of Third World include accumulation, aggregation, collection.

Third World (noun)	assemblage (noun)
underdeveloped and developing countries of Asia and Africa and Latin America collectively	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