Nearly 2,500 years ago, the Greek world was ripped apart. A savage conflict known as the Peloponnesian War pitted many of the Greek city-states against each other. It dragged on for nearly 30 years and cost tens of thousands of lives.

We know a great deal about what went on because a man named Thucydides wrote a book about the war. Called History of the Peloponnesian War, it was the first book of "scientific history." Thucydides' description of the war was based entirely on observation of events and an analysis of human nature. Unlike accounts by earlier writers, the gods didn't play any role.

Early in his book, Thucydides wrote that he believed it would be "a possession for all time." His prediction proved to be correct. Historians, military officers, and many other people still read History of the Peloponnesian War for its insights into politics and human nature.