The Peloponnesian War is firstly a historical account of what happened in the war between the Peloponnesian League and the Delian League. The historical account was written whilst the conflict was ongoing (431–404 BC).Secondly the history written by Thucydides is one of the first works of realist theory in international relations. The story addresses several issues such as human nature and human convention concerning its relationships with power. Human nature itself is drawn towards anarchy as long as there isn’t any human convention or notion of justice. This is an early version of the Hobbesian approach.
The realist strand of IR theory builds on this notion spoken of in Thucydides' history of the Peloponnesian War. The world is inherently anarchic and no one can trust anyone else but themselves. In such a world, the first and most important priority is securing the state. A state needs power, and power is based on self-interest.
When talking about self interest in an anarchic world, it is important to note how the world is a zero-sum game. In the Peloponnesian war, either side can only become stronger relative to the other. This ends in them fighting until both sides are too weak to survive outside pressure from the likes of the Persian Empire, the kingdom of Macedon and Alexander the Great. Athens "empire" also dismantled and they never joined a greek union again.
