Agamemnon, king of the city of Mycenae, not of Greece. .
War was continuous amongst the many city-states and the leagues they formed themselves into, rather like the last 100 years of today, where there is always a war somewhere.
As part of their relationship with the king, the lords always had to provide military support for him. They had to be ready for war.
Athens.
Sardis .
A confederation of Greek city-states.
It caused Greece to be divided.
Which Greek wars? Did you mean the Peloponnesian War, which was fought by the city-states of Athens and Sparta(and their allies)? Athens lost that war. There was the Greco-Persian War, fought between some of the city-states of Greece and the Persian Empire. A stalemate was reached. These are two of the wars that Greece has participated in form or another.
Peloponnesian War.
The city-states of southern Greece had a meeting, appointed commanders and allotted ships and military contingents to them.
The Greeks because they pretended to withdraw and left a wooden horse filled with soldier. The Trojans thought it was a present and got it in the city even though they were warned by a citizen no to. They had a festival and at night the Greeks sneaker out of the horse, opened the gates of the city for the other soldiers and burnt the city down. They had won.
Peloponnesian War.