You cannot win a war without strong economy.
“Because Sparta produced so little of value, the Spartan state simply lacked the funds to supplement its operational capabilities. It could not afford foreign siege engineers or experts (an increasingly dire liability in the fourth century as Greek siege craft both improved and became more technical) and crucially it could not afford a fleet. Spartan fleets, in the end, will be financed by Persia (we’ll come back to this).”
https://acoup.blog/2019/09/27/collections-this-isnt-sparta-part-vii-spartan-ends/