Sentence:  Essentially this imposed two conditions : First , international law had to recognize and be compatible with an international political system in which a number of states <WSD>were</WSD> competitive , suspicious , and opportunistic in their political alignments with one another ; second , it had to be compatible with the value system that they shared . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)