One of the most important elements of the Northwest Ordinance of 1787 was that the Federal government would be sovereign and would expand westwards in hope of founding new states, instead of expanding existing states. This was important for the growth and expansion of the United States (had this not happened, the United States would not be half of what it is now). Another important aspect of the Northwest Ordinance of 1787 is that slavery was prohibited and this was basically the border between free and slave states.
In the beginnings of human settlements, when the Agricultural Revolution had happened and people needed to grow food to survive, the most fundamental feature of the soil was its fertility.
And so it happens that soil is much more fertile and easy to grow food on if there are floods or at least water nearby.
The first map shows the localization of the Indus Valley civilization (3300 - 1300 BCE) and the second is where the Yellow River civilization (3500 BCE-?) was born.
These civilizations were formed in these territories due to the presence of water: in the Indus Valley there were periodical floods that helped grow food, and in the Yellow River basin it was possible to build an irrigation system that sustained people around it.