Why did sparta become allies with persia?

Sparta became allies w/Persia to defeat Athens in the Peloponnese War, and to make good use of Persia's navy. 

An informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.