War... I wonder why humans never learn from history. War is expensive and does not have many benefits for the people below.
But it does benefit the people in power, and even the common people as well to a certain extent.
As winning a war means more human resource (which was critical in ancient times because of low population and high death rate).
It also brings in more land, thus increasing availability of consumable resources and options to earn more funds.
Other than the aspect of "people dying", War had always been more profitable for many people, which outmatches any financial negatives that could occur.