Sentence:  The law of nature governed sovereigns in their <WSD>relationship</WSD> to their own citizens , to foreigners , and to each other in a conceptually unified system . 
Meaning of the word marked with <WSD> tags:  a relation between people; (`relationship' is often used where `relation' would serve, as in `the relationship between inflation and unemployment', but the preferred usage of `relationship' is for human relations or states of relatedness)