The History of the Peloponnesian War is a historical account of the Peloponnesian War (431-404 BC), which was fought between the Peloponnesian League (led by Sparta) and the Delian League (led by Athens). It was written by Thucydides, an Athenian historian who also happened to serve as an Athenian general during the war. His account of the conflict is widely considered to be a classic and regarded as one of the earliest scholarly works of history.
The History of the Peloponnesian War begins with a brief review of early Greek history and some programmatic historiographical commentary. It then seeks to explain why the Peloponnesian War broke out when it did and what its causes were. Except for a few short asides, the remainder of the History rigidly maintains its focus on the Peloponnesian War to the exclusion of other topics. While the History concentrates on the military aspects of the Peloponnesian War, it uses these events as a medium to discuss atrocities, realpolitik, justice, and the socially and culturally degenerative effects of war on humanity itself.