Mesopotamia is located on Asia and in the Middle East, which is now modern-day Iraq. Due to where Mesopotamia was geographically located, it acquired two nicknames. It is true that ancient Mesopotamia is located inside the geographic region referred to as "The Fertile Crescent," which was its first nickname. Another nicknames were The Land Between Two Rivers and Cradle of Western Civilization
The king is basically giving them a license to start a colony. It's like how you can't drive a car unless you have a drivers license, but with colonies.
