We know this thanks to archaeologists who excavated many places and discovered that many early civilizations gathered around large rivers where they could develop agriculture. This was seen in places such as Mesopotamia, India, China, Egypt, etc.
The Freedman's Bureau was created to help former black slaves and poor whites in the South after the Civil War. Giving them education and medical help was very important in helping them recover from the revolution and helped the freedmen to be able to live on their own.
He used this to keep the communists away because they were weaker than us and could not afford to be attacked; we could.
