Why were the tribal leaders and all the nobility interested in military campaigns?

The basis of economic growth and the influence of any state at the beginning of the Middle Ages was income from robberies, the seizure of slaves and the territories of other states.
Due to the fact that the leaders of the tribes made such raids, they enriched their treasury, as well as the pockets of ordinary soldiers and inhabitants of the tribe.
Capturing new territories and winning battles, the tribes received more dependent territories, and as a result, the amount of tribute.
Thanks to this, the influence of the leader grew not only among his own people, but also among the nobility.
The ruler’s brutality and strength aroused fear in enemies.