Explanation:

- The quote discusses the concept of "ingroup" and "outgroup," where ingroup members experience peace and order, while relations with outgroup members are hostile unless modified by agreements.

- This idea aligns with the work of William Graham Sumner, who coined the terms "ingroup" and "outgroup" and elaborated on their dynamics.

- W.G. Sumner: Known for his theories on social groups and dynamics, especially relating to ethnocentrism and the distinction between ingroups and outgroups.

- R.K. Merton: Focused on social structure and anomie, not specifically on ingroup and outgroup dynamics.

- C.H. Cooley: Known for the concept of the "looking-glass self," rather than ingroups and outgroups.

- E. Durkheim: Concentrated on social solidarity and division of labor, not specifically ingroups and outgroups.