What were the three civilizations that developed out Mesopotamia?

How do rivers flood and why is this good for civilizations?

• I've been studying a bit into the three early civilizations: Egypt, Mesopotamia and the Indus Valley Civilization and all three popped up around rivers (e.g. Nile, Tigris and Euphrates, and the Indus).  I read that the flooding of rivers makes it a good basin for civilization but I don't understand why that is.  First of all, what does it mean when a river "floods" in the first place?  How can it be so regular and if not, how can it be controlled?  Finally, how is this good for civilization cuz I know that in 2010 the Indus River flooded that resulted in thousands dead and billions in damages.  Not to mention other floods like the Yellow or Yangze River that killed millions of people over the course of history.  I just don't understand this concept very well so if someone could explain it to me, that'd be great!

• Answer:

  Let's answer the 2 parts of your question in turn. 1: Why do rivers flood? Rivers flood because of an increase in the available water flowing across the landscape, either because of an increase in precipitation or a release of a pent-up amount of water.  In certain parts of the world, there are wet seasons and dry seasons, the former of which brings an increase in precipitation and a correspondingly high amount of water flowing in the river. 2: Why is this good for civilizations: A flooding river brings a lot of rich mud, which is deposited in the agricultural fields of a people group.  This means that the fields will grow more and better crops, something absolutely necessary for an fledgeling civilization.  Complex civilization is defined by one thing primarily: craft specialization.  This is when a society has plenty of food, and some people can devote that time and energy into other crafts, such as art, weaving, metalworking, etc.  Hunter-gatherer societies simply do not have time for people to specialize in a trade, as each person must obtain their own food.  When a society is capable of having food-production specialists who can produce a surplus, the door is open for other specialists to invent and develop other trades, because they can simply buy food obtained by other people. This tends to happen in areas that are very good for agriculture, such as the three river valleys you mentioned.  The flooding means the land is more fertile than other areas, and fewer people can make more food, freeing other people for craft specialization and developing technology.  It creates an interdependent cycle, as the craft specialists depend on the farmers for their food, and the farmers depend on the craft specialists for tools and clothing.  The craft specialists live together in closer and closer proximity, because everyone is depending on one another, which creates cities.