Thucydides (455-395 B.C.) was the first historian in ancient Greece. Born into an aristocratic Athenian family with roots in Thrace, he is famous for writing the History of the Peloponnesian War, the first full work of historical analysis.
Thucydides was himself a participant in the Peloponnesian War, commanding an Athenian fleet in the northern Aegean in 424-423. He was exiled from Athens at the end of his term in office as punishment for failing to arrive in enough time to successfully prevent the capture of the major Athenian settlement at Amphipolis by the Spartan general Brasidas. During his time in exile, he was able to travel extensively and observe the military and political developments in many of the theaters of war. His history is thus particularly notable for its vivid descriptions of ancient battle and detailed accounts of the political debates in his own democratic Athens.
Thucydides is perhaps most well known to modern scholars for his view of politics and the nature of interstate relations. He repeatedly argued, during the course of his narrative, that states should act primarily in their own self-interest. More importantly, while not ignoring more immediate provocations, he contended that the long term Origins of the Peloponnesian War lay in the growing discrepancy in power between Athens and its main rival, Sparta. These views have led many historians and political scientists to regard him as the father of realist political theory.
Thucydides' view of internal politics was ambiguous. While he frequently praised the merits of democracy, and the endurance of democratic societies during times of great difficulty, he also regarded it as a potentially dangerous system, in which uninformed masses could be manipulated by self-serving demagogues into pursuing foolish courses of action, such as the poorly planned and executed Athenian invasion of Sicily in 415 B.C. A strong, statesman-like leader like his hero, Pericles, would thus be needed to restrain the urges of the people.