You are in uni!
You should know this...shouldn't you?
Many states or allies revolted because Athens was trying to set up democracies in their states. Thanks to Pericles.
When a state revolted, Athens would march in to establish garrisons and install democracy. They would also favor those states who are democratic, or go against any state that has another form of government or anything that Athens would like to have. An example would be Samos. Samos had the second largest fleet besides Athens, and when a quarrel between Samos and Miletus arose, Athens sided with Miletus because this means that she has a right to enter Samos and establish a democracy, and take anything she wants.
i hope that this sort of helps...