He set forth the concept of the oceans as free to all nations in his work on the law of Booty. He began work on the rules of war and peace. To reasoning beings, the need for law is self-evident. This capacity leads to a social contract set forth in writing or in customs. The contract differs in all societies but is binding upon all in that society.
Natural law takes precedence over civil law, custom and even divine law.
A family or a ball team is a group but a row of workers on an assembly line or a set of slaves or prisoners working at a task is not a group. In colleges, sororities and fraternities are organized as groups while classes are often impersonal and interactively barren. Central to all group activity is symbolic interaction in which intersubjective understanding emerges. Groups often have status hierarchy which also pre-shape behavior of members. Then there are 'dis-engagement' activities in which people recognize that the claims each has on the other are to be set aside until the next time the 'group' meets.