In Thucydides' History of the Peloponnesian War, the author describes and analyzes the conflict which occurred between the city-states of Athens and Sparta (and their respective allies) from 431-404 BCE. More importantly, Thucydides provides the reader with justification for the Spartan victory that resulted from this conflict. The main reason for the Spartan victory, according to Thucydides, is shown in the ultimate viability of each polis' leader's strategies and projections before the conflict. Prior to any fighting, Pericles of Athens and Archidamus of Sparta (with the aid of Spartan allies) devised net assessments that both believed would provide strategies leading to victory and peace for their respective states. In essence, these net assessments can be broken down into three elements: first, an understanding of the nature of the war; second, the identification of the strengths and weaknesses of the enemy to identify a comparative advantage; and finally, the devising of a strategy to achieve victory. As Thucydides argues, the Spartans did a superior job of net assessment in all three of these elements prior to the outbreak of the Peloponnesian War.
Sparta's King Archidamus took the realistic approach to the potential war: by realizing the inevitable failure of diplomacy efforts with Athens, he instead chose to prepare his own polis for war under the guise of these so-called diplomatic efforts. As he explained in a speech, "If [the Athenians] pay attention to our diplomatic protests, so much the better. If they do not, then, after two or three years have passed, we shall be in a much sounder position and can attack them- (The Peloponnesian War, p. 84).
Secondly, noting Athens' naval superiority, Archidamus was fully aware that a conflict between Athens and Sparta was not an affair that could be ended quickly. Archidamus knew that the Athenians were unlikely to fight an infantry-based war (Sparta's area of military expertise), as Athens' culture, military and economy all revolved around its supreme maritime strength.