History of Mesopotamia
Mesopotamia was first settled by the Sumerians around 3500 BC. They were attracted by the fresh water supplied by the Tigris and Euphrates Rivers that they could drink, use to water their crops, bathe in, travel on, etc. Different cities were built in Sumer, such as Ur, Uruk, Lagash, and Kish. They were called city-states. They all shared the same culture, but they had their own rulers/kings, gods, and laws. They basically acted like their own country, but they were tied together because they were all from Sumer. A city-state consisted of the city plus the land that surrounded it. Each city-state had a large city wall around it to protect it from enemies. The Sumerians were known for inventing LOTS of important things. You'll learn about these in the section called Inventions.
The End of Sumer
Around the year 2500 BC, the city-states all began fighting each other. This left them weak and unable to fight against enemies trying to invade them. King Sargon of Akkad did just that. He attacked Sumer around 2350 BC, and created the world's first empire when he took all the independent city-states and put them under his own control. The Akkadian Empire, as it came to be called, only lasted about 200 years due to internal fighting, invasions, and famine (lack of food).