Soon after the termination of the Peloponnesian war, the strength of Lacedaemon began to decline.

Its military discipline, its social institutions, were the same.

Agesilaus, during whose reign the change took place, was the ablest of its kings.
Yet the Spartan armies were frequently defeated in pitched battles,--an occurrence considered impossible in the earlier ages of Greece.

They are allowed to have fought most bravely; yet they were no longer attended by the success to which they had formerly been accustomed.

No solution of these circumstances is offered, as far as I know, by any ancient author.
The real cause, I conceive, was this.