1. Arab Empire

2. Nomadic Tribes lived in the deserts and cities of Saudi Arabia.
They would constantly fight against each other.
Lots of revenge killing
They would never work together because it was more important to them to get back at each other than to fight somebody else.

3. The Islamic religion changed that.
The tribes converted to Islam.
Because of that they were not supposed to kill each other.
With all the warlike power united, they went out and conquered most of the known world except for Europe.
Religion was the unifying factor