The nomadic tribes of Southwest Asia have influenced the character of the region because ...

Because they are they spread and teach their culture across the region.

Explanation:

The main characteristic of a nomadic tribe is that they constantly move from one place to another in order to seek for new resources.

When they move, they are most likely stayed in one region for a short period of time and communicate with other people in that region. When this happen, cultural assimilation occurs between the nomadic tribes and the local people. Because of this, the activities by nomadic influence greatly influenced the character of the region.