Countries are often compelled to take certain courses of action by the realities of the world in which they exist.
Many factors determine the nature of any given system.
Systemic factors include its structural characteristics, power relationships, economic patterns, and norms of behavior. One structural characteristic is how authority is organized. The international system is based on state sovereignty and, therefore, is anarchical. There are, however, relatively new centralizing forces that are changing the system. Another structural characteristic is determined by who the major actors in the system are.