 The scope of international relations encompasses issues such as globalization, diplomatic relations, state sovereignty, international security, ecological sustainability, nuclear proliferation, nationalism, economic development, global finance, terrorism, and human rights.Studies of international relations start thousands of years ago; Barry Buzan and Richard Little, for example, consider the interaction of ancient Sumerian city-states, starting in 3,500 BC, as the first fully-fledged international system.The history of international relations based on sovereign states and many more types are often traced back to the Peace of Westphalia of 1648, a stepping stone in the development of the modern state system.