How Did Sparta Decline

The Decline of Sparta in 371BC
Sparta has been famous since antiquity for her military strength; indeed, it was believed by most Greeks that if Sparta rose against Attica, Athens would not be able to hold out for more than three years before surrendering. So, if Sparta was considered one of the strongest players in the classical world, why would she fall?
The numbers of Spartiates have long been suggested as the main contributing factor in her decline. According to Plutarch, at the Battle of Leuctra in 379 BCE, a Theban army consisting of 10,000 hoplites met 700 Spartiates. When one looks at the difference of the numbers between the two armies, it is not surprising that one asks "could the fall of Sparta have been because of the shortage
This fault, although it manifested in a number of disparate ways, could be summed up in one word: short-sightedness. This short-sightedness occurred in areas such as its attitudes, its failure to modify the rigid Lycurgus system, its tactical naiveté, its failure to adapt when opponents began hiring mercenary armies, its misconduct, its lack of negotiation and cooperation with its own allies. Although Sparta had great military strength, it dissipated the effect of that strength by obtusely refusing to consider anything outside its narrow field of vision. It was like a bulldog on a single-minded mission, resolutely forging ahead as though no one else were worth caring about not even its own allies. Ultimately, Sparta's incredible and overweening short-sightedness caused it to lose its domination and become demoted from a world-class reigning military power to a much lesser
Sparta simply believed that the Lycurgus system did not need to be altered. Furthermore, they were against Spartans having too much wealth or personal power. As a result, the Lycurgus system's rigidity produced a closed society plagued by the effects of inbreeding. Some historians agree that "the Spartan hegemony 'perished through 'oliganthropia'' - a lack of men. This is not because of a population decrease in Laconia but just a lack of men of the Spartan citizen class who could serve as hoplites, called 'homoioi' or 'Spartiates.'" The number of men that Sparta could call upon to send into battle diminished appreciably during the 5th and early 4th centuries B.C. This was not solely due to reduced numbers of men but also partly because they were reluctant to leave Laconia unguarded and tended to send fewer men to battle than they could have. In the 5th century battle at Thermopylae against the Persians, only 300 Spartans and 1,000 allies held off the massive invasion of Persia's King Xerxes that is estimated to number over 120,000 men. According to Herodotus, however, there were probably 8,000 Spartiates available to be deployed (Scipio,