Umman Manda was the name given to a group of people who lived a very long time ago in a place called Mesopotamia which is now called Iraq. They were part of an even bigger group of people called the Akkadians.
The Umman Manda were known for being really good at fighting and were very strong. They were often hired by people called kings as soldiers to help protect their land or conquer other places.
Sometimes the Umman Manda even took over kingdoms themselves and ruled as kings. They had a lot of power and influence in Mesopotamia for a while.
So, basically, the Umman Manda were a group of really tough soldiers and fighters who were important in ancient Mesopotamian history.