What is the historical significance of Mesopotamia

They created the city called Babylon.
It was at the other end of the Fertile Crescent (the other end was Egypt, other great civilization). Like the Egyptians they were conquered by the Persians.
But unlike the Egyptians, they were not optimistic. They were very pessimistic. Their region was between (Meso) two rivers (potamia. < potamos, river in Greek). They were so pessimistic that they turned their feeble hopes towards the sky. The planet. They became the first astrologists, there ever were. They also became a sort of astronomers. Next to Mesopotamia was a region called Media, where physicians were very good at their work. Mesopotamia started collecting a lot of remedies. They were with the Medes, the best doctors of the time (> medicine). They had ways to communicate with the East and with the West. so, good commerce.
But most of all, Mesopotamians codified the law, many times.

A very advanced system of laws. We know the most famous, the code of Hammurabi. But this code just was the extension and embellishment of the preceding codes.
A reproduction of a part of the Hammurabi code is in Washington DC, in one of the greatest building there (the Capitol?)

Life in Mesopotamia was very much like a modern life, with diversity, commerce, work, religion, laws, cities with big streets.

''By understanding the foundations of the early empires, we can begin to understand how all of it fits together.''

A fair point. It reinforces what's been a very old adage for a long time now. Study history to learn about the past. And in turn gain an interest and basic understanding. Of-and into a variety of other disciplines; and their impact on mankind as it has developed.