Sentence:  More emphasis was put upon the fact that international law was the law of `` civilized nations '' ; Kent and Story , the great early American scholars , repeatedly made use of this phrase , or of `` Christian nations '' , which <WSD>is</WSD> a substantial equivalent . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)