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.