while Sparta became established as the leading power of Greece. The economic costs of the war were felt all across Greece: poverty became widespread in the Peloponnese, while Athens was completely devastated and never regained its pre-war prosperity. The war also wrought subtler changes to Greek society: the conflict between democratic Athens and oligarchic Sparta, each of which supported friendly political factions within other states, made war a common occurrence in the Greek world. Ancient Greek warfare, meanwhile, originally a limited and formalized form of conflict, was transformed into an all-out struggle between city-states, complete with atrocities on a large scale. Shattering religious and cultural taboos, devastating vast swathes of countryside, and destroying whole cities, the Peloponnesian War marked the dramatic end to the fifth century BC and the golden age of Greece. Historic sources The main historical source for most of the war is the detailed account in The History of the Peloponnesian War by Thucydides. He states that he began writing his history as soon as the war broke out and took his information from first-hand accounts, including events he witnessed himself. An Athenian who fought in the early part of the war, Thucydides was exiled in 423 BC and settled in the Peloponnese, where he spent the rest of the war collecting sources and writing his history. Scholars regard Thucydides as reliable and neutral between the two sides. A partial exception are the lengthy speeches he reports, which Thucydides admits are not accurate records of what was said, but his interpretation of the general arguments presented. The narrative begins several years before the war, explaining why it began, then reports events year-by-year. The main limitation of Thucydides' work is that it is incomplete: the text ends abruptly in 411 BC, seven years before the conclusion of the war. The account was continued by Xenophon, a younger contemporary, in the first book of his Hellenica. This directly follows Thucydides' final sentence and provides a similar record, on the topics of the war's conclusion and aftermath. Born in Athens, Xenophon spent his military career as a mercenary, fighting in the Persian Empire and for Sparta in Asia Minor, Thrace and Greece. Exiled from Athens for these actions, he retired to live in Sparta, where he wrote Hellenica around 40 years after the war had ended. His account is generally considered favourable to Sparta. A briefer account of the whole