Thucydides was an Athenian, but had very little reason for offering a distorted view of the war that was eventually won by Sparta.
Jackson states, "Thucydides was an active participant in Athens for a time, he had a network of contacts, while banished to Thrace he observed the war there first hand, and as an Athenian exile he traveled along the Peloponnese" (Jackson, p.175). Thucydides wrote of a Sparta that used an eight deep fighting stance against the Athenians who could not, or did not, adapt to a style that would lead to victory when battling against that type of tactic.
Other army tactics began to be used after the Peloponnesian War, many of which were introduced by the Spartans in order to maintain their military might. One such tactic would play a key role in the battle of Leuctra.
Of particular relevance to Leuctra, however, was the battle of Nemea in 394 B.C. In this action the right wings of both armies began by moving to the right with the aim of encircling their opponents. Encirclement was not new, but the deliberate attempt to prepare for it in the approach march certainly was" (Cawkwell, p. 399)
The Spartan army adapted tactics and techniques designed to overpower, overwhelm or overcome their targeted enemies but their enemies learned from these engagements as well. When Sparta adapted an eight man deep wedge formation that forced their opponents into attacking into the strongest part of the army, other armies adapted the same tactic and took it a step further, sometimes lining up 12 and 16 deep. Sparta in the battle of Leuctra "abandoned their ancient favored depth of eight and formed up twelve deep, and sought to move to their right" (Cawkwell, p. 399) most likely in anticipation of the same movement they experienced approximately twenty years earlier at Nemea. The Thebans, however, did not react accordingly. Instead they piled their army fifty-deep and moved to the left, leaving no room for Spartan encirclement. "It is clear that the Spartans were confronted by a wholly new tactical situation. They fought with great bravery but were utterly out-generalled" (Cawkwell, p. 399).
Where Cawkwell sees the Spartans as being entirely 'outgeneralled" other observers might see a society that had run its course, that had self-destructed by violating its own standards.
An example of one of the primary violations was the one that allowed for no silver or gold currency in Sparta, instead the created iron spits that were to be used as payment for almost every conceivable item. Other societies, however, did not take kindly to iron spits for payment. It became necessary for Spartan government to hold a certain amount of gold and silver in order to send ambassadors, couriers and other individuals outside the country. As Sparta became rich, conquering more territories and city-states the wealth rolled in and many of the officials benefited from this newfound wealth.
This inevitably led to a certain amount of greed and envy, many of the citizens maintained an austere lifestyle only to see government officials displaying, and many times flaunting their newly acquired gains. Many of the citizenry wished to participate and share in that wealth. Classes and divisions were formed in Sparta that had previously been disdained. Such divisive actions would likely cause even more greed and envy, and the government's grip on the citizens would be weakened. Sparta was no exception to the rule, it is tough to maintain a lifestyle as demanding as the Spartan one was without complete loyalty. Citizens who are concentrating on gathering wealth are not likely to concentrate on being trained to go off and fight, no matter how honorable it is. The filthy lucre is more beautiful than death.
These same citizens are probably equally likely to send someone else off in their stead, and most of the time it is not going to be a son that they send.
If the lure of wealth is what keeps them at home, it also allows them the opportunity to pay for someone else to protect them, or to find and conquer new territories. Many times those that are sent in a Spartan's stead would be men from other cultures or countries. Their incentive in accomplishing any objective would be to become a free citizen of Sparta, and that is a lot of incentive. However, would it be enough incentive to fight to the death, as most Spartiates had been raised to believe was the most honorable event in one's life? Probably not, and decidedly not if we are to believe that the battle of Leuctra was fought by only 1000 Spartiates, with the rest of the army comprised of citizens from other cultures.
It makes sense that Sparta was defeated at that time and place. They had fallen victim to the baubles of their own success, never realizing until it was too late that society loves to witness the big boy on the block biting the dust, no matter who that big boy happens to be.
Cawkwell, G.L. (1983) the Decline of Sparta, Classical Quarterly, Vol. 33, Issue ii, pp. 385-400
Hind, a. (2006) Weaponry: It took a humiliating major defeat to convince the Spartans to adopt the bow and arrow, Military…