Athens and Sparta had cooperated during the Persian War, but relations between these powerful states declined throughout the years. The Athenian pursuit of equality in their city combined with their growing domination abroad allowed Athens to attempt to create a land and maritime empire. This was one of the main causes for the First Peloponnesian War. The Delian League was initially established as a naval alliance among the Greek nautical states. Overtime, the aggressive policies of Athens converted the voluntary allies of the Delian League into the involuntary subjects of an Athenian naval empire. When Athens tried to expand their kingdom to the Greek mainland they encountered a series of battles with Sparta and its allies, which started the First Peloponnesian War. After a succession of defeats for the Athenians, their land empire began to collapse and they agreed to a thirty year peace treaty with the Spartans. Athens began to use the Delian League as its own empire. They eventually increased their control over it by gaining power of its treasury. The Athenian Pericles was responsible for taking Delian League funds for various projects. He constructed the “long walls” with these reserves enclosing Athens as well as the port of Piraeus. The Spartans saw this piece of land as an important part of their defenses and believed this gave the Athenians an unfair military advantage. Athens did not allow members of the League to leave their alliance. Each ally was charged a fee for the protection that Athens claimed to provide for them. Various city-states of Greece including Sparta, protested that the politicians of Athens were using League funds strictly for their own city. The Athenian quest for domination became too much and it was not long before Greece was thrown into a long drawn out struggle. Sparta became extremely concerned by Athens ambitions and growth in