You're right, the reason the very first civilization on earth flourished in (modern day) Iraq was because of the fertile land from the two rivers. Mongols did destroy Baghdad, the that was rather long ago -- the main reason the country is doing poorly was because of British colonialism, then Saddam Hussain, Iran-Iraq war, Gulf War, American invasion.... and finally poor governance and spread of religious extremism.

All these things and more collectively lead to what you see right now, the 5th most oil-rich country in the world looking like the poorest one.

You are Iraqi?

Yup! I'm an ethnic Assyrian (you can tell from the flair) - Assyrians are the indigenous people of Iraq, Syria, Iran and Turkey. Our history goes back thousands of years, we claim descent from the ancient Assyrians of Mesopotamia. We are what's usually labeled as "Iraqi Christians" (but there's more to us than just religion - we're a distinct ethnic group different from Arabs or Turks, have our own language and culture.) Although in the past 2 centuries, particularly in 1915, our numbers have dwindled from millions to a few hundred thousands, and we're at a steady decline as more and more people are being killed or are immigrating abroad.

If you'd like to know more feel free to check out these resources: https://en.wikipedia.org/wiki/Assyrian_people
https://en.wikipedia.org/wiki/Assyrian_genocide
https://www.youtube.com/watch?v=7pa54hWROpQ