They wanted to trap and then trade furs with the Native American groups in that area.
The correct answer to this open question is the following.
The geographic feature of Mesopotamia that led to the Sumerians being easily taken over was the Tigris and Euphrates Rivers that made it easy for their enemies to navigate and invade them.
Sumeria was the oldest civilization known to man. Sumerians settled in the middle of the Tigris and Euphrates Rivers in the Middle East region. There, they developed agriculture techniques and learn how to use the flood of the rivers to grow crops in that fertile soil. That is how they prosper for some time until their enemies could access their city-states navigating through both rivers.
It was one of the first democratic governments in recorded history. Letting people vote on leaders was revolutionary at the time and did lead to things like the roman republic, the american revolution, and the french revolution. It lead to a lot of time being spent on the tragedy of being human or self aware. Which of course lead to things like maybe i deserve to have a say in the government.
Later when the Romans took over they looked at all the Greeks stuff and thought huh? maybe this is a good idea. And the rest of course is history.
Hope this helps