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 were competitive , suspicious , and <WSD>opportunistic</WSD> 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:  taking immediate advantage, often unethically, of any circumstance of possible benefit