Athens started that way but progressively moved to a broader , thena radical democracy (however no women or other slaves need apply).
Both states had executive leadership, but both were constrained bythe direct votes of the electorate on important issues.
They became allies when their interests coincided – especiallyin the face of the Persian threat. Then Athens helped Sparta whenpart of its territory revolted.
The split began when Athens began to create its empire bymanipulating the anti-Persian league formed after the Xerxesinvasion was driven off. Athens progressively used the funds forits own benefit and became aggressive throughout the Greek world,which caused a polarisation of city-states behind Athens and Spartarespectively. The split grew and war betwen both blocs ensued (the27-year Peloponnesian War).