http://greece.mrdonn.org/city-states.html

After the Greek dark ages, exciting things began to happen in ancient Greece. Villages started to band together to form strong trading centers. These groups of villages that banded together were called city-states. Soon, hundreds of city-states had formed in ancient Greece. 

TO BE A CITIZEN OF A CITY-STATE: The ancient Greeks referred to themselves as citizens of their individual city-states. Each city-state (polis) had its own personality, goals, laws and customs. Ancient Greeks were very loyal to their city-state. 

The city-states had many things in common. They all believed in the same gods. They all spoke the same language. But if you asked an ancient Greek where he was from, he would not say, "I live in Greece."  If he was from Sparta, he would say, "I am a Spartan." If he lived in Athens, he would say, "I am Athenian." The city-states might band together to fight a common foe. But they also went to war with each other. Greece was not yet one country. Ancient Greece was a collection of Greek city-states. 

Because Greece was not yet one country, there was no central government in ancient Greece. Each city-state had its own form of government. Some city-states, like Corinth, were ruled by kings. Some, like Sparta, were ruled by a small group of men. Others, like Athens, experimented with new forms of government.

Five of the most powerful Greek city-states

Athens , Sparta , Corinth , Megara , Argos 

http://www.historyforkids.org/learn/greeks/war/index.htm

Ancient Greek Warfare

Wars were very common in ancient Greece. The Greeks lived in little city-states, each one like a small town in the United States today, with no more than about 100,000 people in each city-state. These city-states - Athens, Sparta, Corinth, Thebes - were always fighting each other over their borders. Often they would get together in leagues, a lot of city-states together, to fight as allies.
Sometimes other people invaded Greece, and then there would be wars to defend the city-states from the invaders. Sometimes the city-states fought together, and sometimes they didn't.
Then again, sometimes the Greeks fought in other countries. They invaded other countries and took them over, or they raided other cities and took their stuff. And they often fought for pay, as mercenaries, when one foreign country fought another (more on this here).

City-States

A city-state (what the Greeks called a polis, which is where our word politics comes from) is like a very small country, with just one city in it. There are still some city-states in the world today, like Monaco or Luxembourg. But in antiquity and the Middle Ages, city-states were very common.They might have any of a number of different forms of government.

The Standard of Ur, from West Asia (2000 BC)

The first known city-states were in Western Asia, where there seem to have been many of them throughout the Bronze Age, sometimes unified under a leader like Sargon of Akkad, and sometimes not. Uruk is one example of these Sumerian city-states. These city-states seem to have been ruled by kings, with councils of noblemen for advisors, as we see in the Epic of Gilgamesh.

In 490 BC the Persians attacked Athens. Everybody was very frightened, because the Persians were great fighters. Some people thought Athens should go back to the old system of government, the oligarchy, in case democracy didn't work well enough. They thought it would take too long to make decisions in a democracy. But they didn't go back.

All the men in Athens marched out to meet the Persians at Marathon. They thought they would lose. But the Athenians fought in the new way, with the wall of shields, and the Persians were still running and yelling. So the Athenians won!

In 480 BC the Persians, with their king Xerxes (ZERK-sees) attacked again. This time most of the cities in Greece banded together and formed a league to fight the Persians. They lost their first battle, at Thermopylae (therm-AH-pill-aye), but they won after that, at Salamis and again at Plataea (plah-TAY-ah). Again the Persians went home defeated. (More on the Persian Wars).

The Athenians convinced the other Greek cities that they needed to keep the strong Greek navy together in case the Persians came back again. At first everyone thought this was a good idea, except the Spartans, who refused. Then the Athenians said to the other cities, "Don't bother sending ships and men for the navy anymore; that is too hard. Just send money to Athens, and we will build ships and defend you against the Persians." So a lot of cities did that. But the Persians did not come back.

Greece was not alone in the ancient World. Egypt was flourishing. Other civilizations were developing around the Mediterranean. One of the largest and most powerful was the Persian Empire. 

The Persian Empire was huge. It stretched from the Mediterranean Sea all the way to the Indus River in Pakistan.  The Greek Empire was tiny. It covered the small area of the Greek peninsula under the word Greece on the map above. 

When Persia turned her eyes on Greece, they had no doubt that the Greeks would be easy to conquer. They were so outnumbered - what chance did they have? What the Persians forgot was that the Greeks were incredible warriors. Athens had a wonderful navy, with ships that were tiny and easy to maneuver. The Spartan army was fierce.  

The Persians came three times, each time convinced that they could easily conquer ancient Greece. Each time, the Greeks drove them away. During the third battle, the Greek navy led was able to toss burning wood aboard the huge and heavy Persian ships. The men had to abandon ship. Those who made it to shore were greeted by the Spartan army. 

The Greeks took the day. The Persian threat to ancient Greece was ended. 

The Battle of Marathon

Ancient Greek Wars

The Persian War

Persian Wars

Xerxes (Persian Wars Interactive)

Free Ancient Greece Presentations in PowerPoint format