Today I presented an overview of the Persian Wars. Your sources, Pericles' Funeral Oration, and The Melian Dialog present further data on the Athenians in the 5th Century. Athens was the great democratic state of Greece, but what did that mean? How did it govern, and what were its institutions? Beyond that, when it obtained control of the Delian League (which subsequently became the Athenian Empire), what was the nature of that rule.
Athens and Sparta went to war largely because the Athenians continued to expand their leadership of the Greek states and the Greek cause against Persia, but this was not always a benevolent rule over the states within the empire. Examine any aspect of Athenian control of its empire, its war with Sparta, or its government in the 5th Century BCE; you can begin with the questions I have outlined above.