Ancient Greece (500 BC-100 BC demonstrated an early example of a state system, when many small Greek city-states such as Athens, Sparta, Corinth, or Ephesus established extensive relations and an informal means of discussing the
major issues of the day. With small populations and territories and a lack of institutions such as international law, diplomacy, or international organization, the Greek state system was instead based on a shared language, culture, and common religion (Jackson and Sorensen, 2013: 12). These are the basic features that most distinguish it from the modern international system established after the Peace of Westphalia.