Thucydides 
The History of the Peloponnesian War 

The classic history of war between Athens and Sparta. According to Wikipedia: 'Thucydides (c. 460 B.C. – c. 395 B.C.) was a Greek historian and author of the History of the Peloponnesian War, which recounts the 5th century B.C. war between Sparta and Athens to the year 411 B.C. Thucydides has been dubbed the father of 'scientific history’ due to his strict standards of evidence-gathering and analysis in terms of cause and effect without reference to intervention by the gods. He has also been called the father of the school of political realism, which views the relations between nations as based on might rather than right. His classical text is still studied at advanced military colleges worldwide, and the Melian dialogue remains a seminal work of international relations theory. More generally, Thucydides showed an interest in developing an understanding of human nature to explain behaviour in such crises as plague and civil war.’