The occurrence of water (big river) and close civilization.

 The world's four major civilizations have something in common. It all occurred in the large river basin. Egyptian civilization emerged in the Nile River basin, Mesopotamian civilization in the Tigris and Euphrates basins, Indus civilization in the Indus River basin, and Yellow River civilization in China in the Yellow River basin.

  It was easy to get water in the large river basin. Water is indispensable for people to live. Today, water supply is installed in each house, so it is easy to get water, but in the past, water had to be drawn from far away or used by rainwater. So people began to live together by the river, which was easy to get water. Water was essential when farming. This is because it was much easier to water rice paddies and fields when the river was close.

  In addition, there were many wide and fertile plains in the large river basin. This is because the river moves oily soil from the upstream to the downstream area. In the wide plain area, the land was not so hard that I could farm with simple wooden tools. There were no rough mountain ranges, so it was good for people to live together. In addition, thanks to the warm climate, grains such as barley and wheat grew well.

  Of course, a large river flows, but there are places where civilization has not occurred. China's Yangtze River is larger than the Yellow River and has abundant precipitation. However, it is difficult to farm because of the lush forest and humidity around it. The same goes for the Ganges River in India. Many people lived around the Amazon River in South America, but it was difficult to farm due to the high temperature and thick jungle. So it was difficult for civilization to occur.